This very reason is why the DPS breakdown is supposed to place Rogues, Mages, Warlocks, and Hunters at the top of the charts. If you play right and there isn't a huge gap in the gear department than this should be happening regardless.
Throw in the fact that Mages, Warlocks, and Hunters are all ranged DPS, and you find yourself some Job security. I have yet to find a boomkin score consistently higher than 3500 on boss fights, and even that was the best Boomkin I've come in contact with. With Mages in similar gear putting out 500-1000 more DPS on the regular, the demand for more than 1 Boomkin falls off quite quickly. Same goes for more than one of each type of Shaman.
With a predefined raiding group, all this really will do is allow you to raid when, in another circumstance, there weren't enough Tanks on for Construct quarter, or, when a Feral druid isn't invited to Malygos because he isn't ranged. I really think it will help alleviate some of the importance of certain class types.
My question is why they are making it for only 80s? Finding real Heals and real Tanks for grinding up is a HUGE pain in the *** - this dual spec thing would make it much more bearable.