I would probably swap an arcane Mage for the second dps shaman. You get the dmg buff, Int buff, portals, and good dps.

The disc priest could probably heal the whole party and you could have the resto shaman dps with LB also (probably not a huge dps gain but with earth shield riptide, PW Shield, Prayer of Mending, and renew I doubt you will need too much healing).

As long as you can dual spec the priest and the resto shaman, I think you would have a very flexible group.

This is all based off of what Cata is like now. I have not really been following how this will all work out in MoP.