I just want to say that I think any idea of us getting an actual focus bar is almost impossible.
We're still using the same spells as elemental and resto, and that's where the problem lies. For enhance to go this route, the "energy talent" would have to be at the beginning of the tree, or fairly early on, otherwise leveling as enhance would be insane.
Taking that into account, they can't possibly put it early, else Resto/Elem get to talent into it and use a never-ending system for heals and spell dps. The only option then is to put it deep, breaking Enhancement until the ripe old lvl of 50 or so.
You really can't say "uses x energy or x mana"... it has to be one or the other, for the same reasons of abuse listed above. Alternatively, you can't just say that all shocks/SS/LL/LS use energy instead of mana, because you now give resto the option to have shocks on an entirely different resource system, saving mana for heals.
As I said previously, the only option I see for this is to either have an early talent that greatly buffs passive mana regen based on agility/haste, or as someone else mentioned, hard buffs to imp stormstrike and the like to return mana on use.