Stash for Stuff
It's been said multiple times, but I feel a stash for inventory item you wish to keep (but not carry) needs to be implemented. Whether it is in a fixed location (e.g. the book seller in Novigrad has a chest he will let you use Vivaldi has a vault in his bank he lets you use) or accessible from a series of locations (every inn keeper has a magical portal they can access) makes little difference.
I've seen this request multiple places mainly concerning the Witcher school equipment sets. There is a loading note telling players to hold on to them, but carrying several sets of armour tends to clutter the inventory. So while waiting to upgrade them, they just get in the way.
Additional changes which I feel could help:
Create a separate tab for Alchemy creations. I don't like digging through notes, bread, beer, raw meat, etc in order to find a Killer Whale potion
Separate tab for Upgrade and Repair items. Runes, glyphs, and repair kits
Fix the Demetrium bomb glitch. It has turned Geralt into a God, remove the challenge completely. And before I noticed, all my saves had god Geralt in them, and I really don't want to redo the dozens of hour I've already played