That's exactly what I was thinking of doing keybind wise. Then I figured if I needed to tank anything with duration, I could simply make the priest the main and the warrior the alt for that fight. That would let me concentrate on raid healing via click addons and I can just bash a couple macros to maintain the warriors move set. A simple cast sequence shielslam, revenge, devastate, devastate macro, a shield block and a heroic strike key would suffice for most tank and spank fights. Or I suppose I could just make myself the main tank healer and let the other healers worry about healing beyond that. That is probably the most logical solution.

Aside from this PvE stuff. Could anyone shed some light on PvP viability using a melee and healer toon?

PS I tried boxing 4 mages at the same time using trial accounts. That seems infinitely trivial compared to using different classes. Very fun though!