Multiplayer overhaul, specifically pvp and chalice dungeons. PVP needs more dedicated areas, or arenas. Hell, make bell maidens random in any area (Maybe not the first though). Anything to make pvp a bit more common. And tone down the invader HP reduction a bit, too. Maybe just lose 1/4 of their health? As for chalice dungeons, you should be able to summon somebody and have them be able to run through the entire dungeon with you (All 3 depths, and bosses). Maybe give them gems for bosses. I don't know how it'd work (Maybe after small root chalice for coop) but I'd like to be able to run through a random dungeon with a friend, and then run through their own random dungeon with them, instead of the tedious nightmare that currently exists. And no insight use until summoning works.
Arcane builds need something instead of bullets. I don't know how this would balance out ( Some of the spells are strong as fuck) so maybe they could bring back the charges mechanic for spells. More arcane weapons, and possibly a regain system for charges/ mana bar (Only works with your melee, to encourage aggressiveness even with a magic build, where normally defensiveness works better). The regain with melee would be great, because if there was a charge system, there probably would not be many items to regain them, and mana would have to be balanced to avoid spice spam like it DES.
Lamp reworking, you should be able to change checkpoints on already lit areas without going to hunter's dream, you should be able to refill consumables, and respawn enemies. Maybe porting between them too, but that'd be unnecessary.
Two things not big enough to include are more lovecraftian enemies like the byrgenwreth bug-heads, and item descriptions on loading.