I think the best group composition for 10-boxing for MoP for AV / IoC would be 5x Death Knights + 4x Retribution Paladins + 1x Holy Paladins. Maybe exchange one paladin for a priest instead.

DKs get battle rez, lots of AoE ranged damange, great cooldowns and death grip. Ret paladins will get a ton of group self healing, plus with bubble, Hand of Protection, Freedom, Kings, Mights, auras - they add a ton of utility to your DKs.

Personally, I am looking forward to having my 5x DKs use Rocket Boots + the paladins casting Freedom on each DKs. They will be unstoppable.