This game has progressed to the point where every class should have access to more than one dungeon role. The MMORPG genre is progressing beyond the need for a pure class anymore. Barring the removal of the triumvirate of dungeon roles (Tank/Healer/DPS) or the addition of new ones (Support/Controller), a lot of people suggest a fourth spec be added. Until recently, I was in this camp. While this can be a fine idea if implemented properly (as it has been for the druid), not every class needs a 4th spec such (for example, paladins) and there is the difficulty in balancing what would be the equivalent of 3 and 2/3rds classes (especially since the developers continue to hold onto the archaic notion that you have to have same abilities in PVP that you do in PVE).
So baring giving only some classes full specs (which would be unfair to classes that didn't get them) or adding a bunch of specs that are simply a different way of doing the same job (i.e. melee hunter or ranged warrior dps), how can we finally give every class access to more than one dungeon roles?
And then I realized that Blizzard has already shown us how they could do it if they chose. When Mists of Pandaria launched, Warlocks found that one of their specs could actually tank nearly as well as a lot of the classes that are built as tanks . In fact, if they gave them access to the Vengeance mechanic and maybe some additional defensive cooldowns, there is no reason why they shouldn't be considered full tanks and be able to queue as such. But would such an idea work for other classes that need access to additional roles? I believe so and not only would it remove the archaic idea of a pure dps class, it would be a lot easier to balance than a whole spec.
For example - Survival Hunters could have access to a 'Glyph of the Sentinel' that would not only increase the armor and health of their pets, but grant other abilities that would make them a ranged pet tank (as opposed to the Warlocks Glyph of Demon Hunting, which works better in melee range). A healing role could also be added to Beast Mastery by using the glyph idea or even a combination of a glyph with a certain type of pet such as spirit beasts or something not currently tameable like fey dragons, granting abilities that pet and its master uses to heal, rather than DPS.
Rogues could get a 'Glyph of the Skirmisher' that would let one of the specs be a kiting/evasion style tank. (Rogue is one of the classes that I haven't played beyond a few levels, so my knowledge of them would be limited)
Mages could use a 'Glyph of the Chronomaster' to turn their Arcane spec into a discipline style healer using shields and time manipulated heals (HoTs based healing as time speeds up the bodies natural cellular regeneration to superhuman speeds).
However Blizzard does it, it is past time for all classes have the ability to perform more than one role in this game.
(note: I also posted this on the official forums as well, but I expect a better quality of discussion here)