Difficulty/Setting dials: Configuring ADOM explicitly (for your personal perfect enjoyment) and implicitly (to create platform-specific game variants).
While I'm quite comfortable just playing traditional ADoM in the classic Roguelike style (because honestly that's what I'm used to), I think it's good to have options for people who want an easier or harder experience than baseline. I think ADoM did a good job of that. I don't think there should be differences based on platform (assuming by platforms you're talking about different systems/consoles).
Everyone should have the same experience.

Senses in roguelike games: blindness, deafness, muting, being invisible - the pros and cons of these details.
I would like to see some more exploration into this. Give us more use of the senses. Skills to let us hear more (maybe listen to a door to try and guess how many monsters are on the other side).
Maybe a blind fighting general skill that would help anyone who's either blinded or fighting in the dark. Possibly some sort of infravision for certain races that lets them detect heat up to a certain distance (might let them detect warm blooded creatures a few spots away, but wouldn't show items unless they're hot). Being blind would avoid any "gaze" type effects, naturally. And could be tied in with hearing to give us a small "sight" range. Working with the blind for many years, I can tell you that most are still plenty aware that there is "something" nearby, even if they can't tell you what it is.
As for being mute... one thing I've always wondered, is how loud are we in battle? I mean, swords and armour clanging would make noise, naturally. But if you get hit, would you not scream? Or make some sort of sound? Animals certainly do. This could be used in some way. Maybe make some creatures more sounded dependent for seeking out targets.
Invisibility is very powerful, and naturally should have some sort of downside. I think a base hunger increase makes some sense, and is an easy balance. There could also be temporary ways of overcoming it. Like a Goblin tossing a potion at you when you suddenly vanish and being able to see your soaked outline.
Merchants could also refuse to deal with potential thieves who show up invisible. Some sort of magical security system? Maybe your invisibility is negated when in a store? Or you're simply barred from entering.

Item status: cursed/uncursed/blessed versus a much more advanced system.
Personally, I like the current system. It's simple and straightforward. It might be interesting to look at making the c/u/b effect more based on the intended effect of the items though.
A potion of blindless for example. It's supposed to blind you. But if it's blessed, it should blind LONGER, while a cursed one could remove blindless (basically doing the opposite of what it's intended to do). Similar effects could apply to anything really. Many bad things should basically get better by being cursed, as the curse is supposed to flip its effect around (same as cursed good items give you a bad effect).

Item management: weight versus slots versus nothing at all?
Again I like the current system. A standard weight management system that's not overly complex and makes things pretty simple.
Having slots tends to get very arbitrary with values. You'll see many games where you can carry X amount of items at a time, and it makes no sense when things like scrolls take up as much space as armour.
The current system works. And could be built upon. Maybe give us "quick slots" of some sort (easy access pouches on our magical backpack of carrying that we obviously have) to allow us to use some items with less searching and fiddling about.
Also perhaps having equipment layouts that we can save. It would still take the appropriate amount of time to change gear, but we'd be able to change our setup with a button or two instead of going through out items one by one and switching things manually (helpful for when we know we're going up against certain enemies).

Hunger: should we feel it?
I think that slight penalties would make sense. When you're hungry, maybe you lose concentration, have some trouble reading scrolls/spellbooks.
Being bloated could slow you down, make you a little lazy (maybe a weakness to sleep effects to boot).

Movement: diagonal movement versus straight movement.
I don't think there should be any different between the two really. The 8 basic directions should all effectively be the same.

Internationalization: translating Ultimate ADOM into other languages.
As many as possible, naturally. Though perhaps the community can help with that?

Item statistics: how many and which do we need when?
I like the current system. But being able to "look" or "examine" items would be nice. Get a more detailed description of things (maybe with pictures) same as with monsters.

Long actions: how important are actions that cause more than one turn to pass?
That would usually come down to eating, reading books and changing armour. The current system where they can be interrupted makes sense.
While changing armour, naturally that time when the old armour has been taken off and the new stuff isn't on yet leaves us quite vulnerable. But it's often done somewhere safe, so it's not too big an issue.
I figure things like cooking, bridge building, fletchery, etc, would also apply, but again, you're not generally doing it when in danger.
Perhaps while in the wilderness we could get a "camp" option. Where we set up a camp to prepare things, while not doing so could result in random attacks?

Size: of items and monsters: do we care? And how much?
For items, the size is generally taken care of by weight. We're not going to lug around as many two handed swords as daggers, naturally.
For monsters, I think having monsters that take up more than one space could be an interesting mechanic, but would probably be a pain in the butt to program properly.
Right now having things like giants and dragons simply having huge corpses works well enough. And their general weight would apply to things like ice over water and such, but there's not much where weight matters.

Permanent rewards: how should permanent modifications be handled in the future in order to reduce the urge of grinding?
If you're talking about permanent rewards that last between characters? There is potential there, but it can also be easily abused.
I think one thing that could work is a inheritance system. Make it by race (for it to make any sort of sense) and only applies to characters who actually leave the Drakalor Chain. A character makes it out and is allowed to select one item to leave to their heir. So the next character of that race would be allowed to choose whether or not to inherit what's left from before. It shouldn't be required, just an option. And only one item per race (so if you clear it with a human and leave an item, then the next human who plays doesn't take it, when they leave you could choose whether or not to overwrite the heirloom).

Another option I think might work is setting up some sort of starting town. Something that is part of character creation. Where you get X amount of resources to get starting gear. You could have it so that victories with classes/races and completing specific quests in game and certain endings, could unlock new options for character creation. Nothing that should be very powerful, but simply "more" to choose from. Maybe winning with a Wizard unlocks a book store, so future starting characters might be able to choose one of a few basic spellbooks to start with. All starting stuff would take resources, so you couldn't just deck out a character, they'd have to pick and choose how to start. But it would give a bit more variety on starts.

Picking up and dropping items: Manually, automatically or a mix of it?
I don't see anything wrong with the current system. Works great.

Graphics: 2D versus 3D (and what's with ASCII)?
I like the graphics as they are now. Honestly, ADoM doesn't need to be in 3D. It's really just not that complex. And I know a lot of blind players who enjoy the game, adding more graphical depth would be hard on them. They basically play in ASCII mode because it works well with screen readers.

Crafting: how would a smart and fun crafting system look like?
Salvaging: what else can you do with items besides dropping, destroying, carrying or using them?
These really go together. Crafting is something I'd love to see expanded on. Give us options. Tons of options.
I'd love to see us be able to craft specific types of items (weapons, armour, boots, cloaks, etc). Made from various materials. We could learn the "blueprints" for an item by salvaging an item. Perhaps really complex items could need more than one taken apart until we truly learn how to make it. So take apart say a dagger, and you can make one. A crossbow however is going to be more complex to build.
They could all have appropriate skills (smithing, woodworking, fletchery, leatherworking, etc). So characters could focus on skills that would help them most (a wizard might pick up weaving and make robes, but they'd have less use for smithing).
And maybe give us item parts that we could craft and put together. So say different hilts and blades that we could combine to make swords. So we make individual parts of a weapon focused on different aspects (maybe a sword blade that's more durable, or designed for more damage, or serrated for bleeding effects, etc). And then hilts that might improve accuracy, or attack speed. Could lead to an epic amount of customization.

Alchemy: Beyond potion recipes. How about salvaging items for their elemental energies and using those to buff spells, talents and other items?
Getting magical components could be interesting. They could be used to enhance items, either temporarily or permanently (with a lot more skill and resources).
Could also apply to corpses. Perhaps you could dissect corpses into base groupings. So say, reptile parts (lizards, salamanders, lizardmen), canine part (dogs, wolves, etc), specific race parts (dwarf, elf, dragon, etc). Those could each have their own range of effects, enhanced by what they came from. So say giant parts could apply strength bonuses, strong types of giants would give parts with bigger bonuses. Dragon parts could apply weapons with elemental damage or armour with defense, and each type and age of dragon would change just what and how powerful the effect is.

Modding: What's a good modding approach and how much do you want?
Honestly, I don't think modding is really needed if the base game offers enough core replay value. I've never felt an urge to mod ADoM because each experience is still fully rewarding. Meanwhile some games get quite stale after a run or two.