An interface that shows items on self and on floor as one (ones on ground preceded by an (F) perhaps, and/or under its own submenu, or maybe this is determined by what filters are applied); allows you to tag items as destined for floor or self, and then carries out all the drops and pick-ups at once. Maybe have 'perform drops' and 'perform gets' as options for that interface so that you have to take two turns to commit both sorts of change.

Also the specifics of this idea aren't written in stone, it's more the germ of an idea, I hope it can be evolved into something workable.

*EDIT maybe arrows show where items are destined, and you apply a single 'move' command which creates a right arrow for items in inventory and left arrow for items on ground. Applying it again untoggles the move action and nothing will happen once the changes are commited. Maybe just have an asterisk on the right when the item is currently on the ground and an asterisk on the left when it's currently in inventory. Also quick hotkeys inside the menu to filter to just ground items and just inventory items (and the old extended drop and pickup keys take you to this unified menu with that prefilter on). If the item fails to move the arrow will remain, perhaps with an X in the middle. Perhaps you can also move items up and down to express priority and items that won't move due to weight issues will be greyed out in advance? Just throwing ideas at the wall, here.