It feels really messy when everything goes in the same bar, spells, abilities, items, ammunition, everything. It could be sorted better.
And because casters end up getting a lot of spells, I would like spells to get their own interface. Something that sorts all prepared spells cleanly by level and has a more elegant solution for up-casting using a higher level spell slot than creating a separate icon for every possible up-cast spell combination.
Completely agree, the hotbar is too much hard work, I have different level spells mixed up with items and i have to give each tiny item 1 by 1 to find something useful and to understand the spell level. Spells and items are very much different things and a player thinks about them differently, so why put them all together in the same bar?