That is because they are likely limited to Mist elves/Chaos Knights respectively.

Maybe, but for example the gloves of St. Montojja seem generic enough to be generated for everyone.

Those are likely duelist crowning only.

Justifier is also for paladin crownings only, and useless for other classes, but it can still be randomly generated (I've received it as an item drop in GY:2, to add to the insult :p). On that regard, I believe the new artifacts should be able to get randomly generated following the same rules as all random artifacts, although this could be a deliberate balancing decision (you want the awesome chaos knight artifact armor? Play a CK and deal with their disadvantages).

I had the silver key generated with a barbarian too.

i think maybe the armor can stay as a CK only item, but the staff of creation / moloch boots / rapier of needle should definately be generated.

I think all the artifacts should be available for random generation, myself.

I don't think that all items need to be available randomly.