Pure hunter teams (and even 4xHunter+Healer teams) died at the end of Burning Crusade. I ran one. I've posted extensively on the issues with multi-hunters, which you can find if you use the search function.

There are no new gameplay or class mechanics coming that significantly change their viability. In fact, one can argue that they will be even worse than ever since Blizzard is making changes to make PvP combat a little slower.

Hunter defense mechanics are very hard to multibox and they have incredible problems dealing with melee AoE damage (and just AoE in general). In PvE, the game has changed so much that the pets are no longer as tank-like as they once were.

Before you go too crazy with a response about PvE performance, I will say that if you over-gear content, then anything is possible.

Multi-hunters were so very fun and awesome... in Burning Crusade. Since then, they are sub-optimal for boxing in almost any game situation.