The biggest obstacle is the number of abilities, hence why I suspect they'd need to redo the UI. Back when I played, you NEEDED 10 just for most of your regular abilities, and there were a host of situational side abilities or toggles for auras and such. ESO handles that dilemma with the weapon swap giving you 2 bars of 6 abilities each, so you're limited to 10-12 period. STO(which is as bad or worse than WOW on situational or regular use abilities) handles that by letting you set a bunch of abilities on auto-fire so they fire off as soon as they're off cooldown. Unless they've really pared down abilities in WoW, I don't see either approach being a fit for WoW's controls on a gamepad - perhaps maybe a macro-builder? It'd be a bit clunkier than manually running your rotation but that might be a solution.