I think it would be cool to add a feature that would allow you to "hot swap" your abilities.

Example/Explanation:
Naix
Q - Rage / E - Feast / R - Open Wounds / F - Infest

Hot swapping would allow me to re-arrage the abilties however I want, on the fly. So lets say I wanted to switch around Feast & Open Wounds, I could press and hold a series of keys and drag and drop the abilities over so that my abilties would be the following:

Naix - Hot Swapped
Q - Rage / E - Open Wounds / R - Feast / F - Infest