It would be excellent if we could define a different set of controls for each class, similar to how TF2 will automatically load a different named config file for each class. For example, I would want the yellow skill to be easily accessible if I'm playing assassin (cloak), but it may as well be bound to scroll lock if I'm playing tank (deploy).
I know this was something people wanted for the XBLA version too, though it wasn't feasible for that platform. It should be possible to do this for the PC, but it'll have to go on our list for future features.