Well, as experience goes, one of my teams is Fury Warrior, Combat Rogue, Hunter, and Tank/Healer (depends on which I want to use for the last two). Once you get the positioning down, Melee DPS work fine, and generally speaking, encounters shouldn't be TOO difficult with all melee. That said, I skipped Heroics and went straight in to Naxx and VoA, so I can't say with any degree of certainty how viable heroics are. Most should be viable, and all 70-non Heroics have been cleared.