Well, from what I can see....melee with 5x shammies shouldn't be an issue at 70 being all elemental builds. Hardly any damage comes from melee at 70 if spec'd elemental. The only problem I would see with melee is the fact that melee usually is the best option for leveling efficiency....and yes melee is difficult to multibox.

So, if one can level without melee or deal with the difficulty of melee...and then spec elemental at 70...it should be no problem.

In pvp and not having a lot of aoe options though besides fire nova totem....facing targets to chain lightning/shock/lightning bolt is going to be difficult once they are up on you.