Tobold has an important post up about hypothetical combat systems for MMO games. I think he hits on most of the important parts, but perhaps underestimates how difficult it is to make a decent combat system. Execution is Blizzard's trademark, and a conservative combat system that functions perfectly will always be better than an innovative one with many bugs.
But I think he's on to something. WoW will probably be considered the pinnacle of the hotkey style of combat, but with new technology, different styles will be brought forth. Check out Tobold's post--more later.