I believe that the class identity reason is actually a poor one for a couple of reasons.
1) We already have dual specialization meaning we already have access to 2/3 of all the class options. The new talent system that came with MoP made it so you don't really need to change from PvE to PvP of the same spec anymore since you can just use books to change glyphs and talents. A raid leader that would ask to switch specs if tri-spec were to do it would ask you to do it anyway. This is a case of going halfway between "class identity" and giving us the option to change at will.
2) *YOU* give your class the identity, not the specs. *YOU* are the one that chooses to play as a shadow priest and not do any healing. *YOU* are the one who loves to specialize in tanking as your role. *YOU* are the one that may choose to play a different spec. I have 2 level 90 mages, one is my Frost Mage, the other is my Fire Mage. They both have the Arcane spec, but I consider neither as Arcane. Same idea if this were spread to all 3 specs.
3) You can already access all 3 specs with a small gold dump, and the hassle of keybind swaps. This part is just poor design in order to retain "class identity", because it's easy yet a bit of an annoyance to have to do for those who want to switch constantly.
I also believe it would look a lot cleaner interface-wise to merely swap from the 3 class specs rather than unlock spec 1, then choose between 3 specs, unlock spec 2, then choose between 3 specs. It should be unlock spec 1, choose from the 3 specs, unlock spec 2, choose from 2 remaining, unlock spec 3, get that last one. Guardians would get the 4 specs instead. I know this is hard to visualize, but it would make things feel like less of a hassle and less confusing for the newer player.