I would like to see a banking system for the money in the game. If money has weight putting in the bank will let you gather interest at a low rate. If the bank is in the characters home town or the town where your house is you can invest in the town.
If the blacksmith needs money to expand his business you go to the bank, get a message from him and you have a choice to help him or not. Then after he expands you are given a choice of reward. Your investment back after 15 gaming hours (You have to play for 15 hours) to get your money back with 10% interest or you receive a discount for the rest of the game or a high powered weapon on top of an expanded inventory.
I don't like the grid system I prefer the Fallout 3 inventory system based on weight. I am a pack rat so stuffing my pockets with everything I can get my hands on is a big thing for me. It is far simpler than a grid system. I am playing borderlands and I feel like I am in the inventory system for ages trying to decide what gun to drop. I want to avoid if that is at all possible.
I like the idea of upgradable packs like Hypevosa mentioned. I like the room saving items but with the added crafting ability to the game you would want to carry more as you don't know if that thing you are leaving behind is rare herb that can grant you a high level healing potion. But if I had the choice I would like the Fallout 3 system.
How the inventory is displayed is important to me. I like the Tales of Graces F approach where all crafting ingredients are on one page and potions on an other and weapons and armour on another.