Controller Mapping
The ability to freely map controller buttons would be wonderful.

Currently, for example, lock/unlock target can only be mapped to either of the two thumbstick buttons, and not to any others.

I don't quite understand why this shouldn't be mappable to any of the available buttons on a controller.

Cross Hotbar UI
I like the cross hotbar. Its great for PS3 players, and people like myself who use a controller on PC. Switching between cross hotbar sets mid-combat could be improved upon if when quick-swapping sets by single clicking the set swap button it only cycled through bars that were NOT set as shared.

This way, you can set it so that when quick-swapping sets you only toggle between cross hotbars with actions relevant to your current class with a single button press, and can still select shared hotbars by holding the switch sets button and selecting the corresponding set from the popup menu.