Today Bornakk, a blue community poster, said that right now all Blizzard intentionally wants is to have two specs be available, but that they "...want to see how the system works out first," before considering triple specs. I think it's pretty safe to read between the lines here and take it to mean that it's possible and has at least been discussed by Blizzard to some extent if community people (and not a developer like Ghostcrawler) are already talking about it. Remember here that community folks usually don't talk about development related things without running it by or hearing it from a developer first.
Triple specs would offer even more flexibility to play the class in whatever way is possible. A druid would be able to switch between a healer, tank, and caster role in a single instance / raid. A paladin would have the same amazing flexibility. While each class right now has at least two specs that can really shine in specific situations, triple specs would allow three-role hybrids to become amazingly powerful characters.
Of course, some might see that as a reason not to allow triple specs. I'm sure that thought has crossed the minds of the devs as well. After all, if you can do everything under the sun with your one Paladin, why play a Warlock In Plate Death Knight?
Bornakk goes on to say that respeccing has always been part of the core came, and that they want to keep it around. They want to obviously improve the respeccing process, but not completely replace it. From a gameplay perspective this makes a lot of sense as well. We need to have some sort of consequence and reward system – a game in god mode is no fun after all. Want to play a healer when you're speced for DPS and tanking? Pay 50g. This two spec system coming up in patch 3.1 is obviously better than it was before dual specs, but the cost/reward system is still there.
Bornakk makes the additional point that if they were just going to remove this cost/reward system, then they might as well just allow quad specs or what have you.
This is an interesting subject that I think many people will want to keep an eye on. While I don't see triple or quad specs coming out anytime soon, I think it's obvious based on Bornakk's comments that we shouldn't just write them off. World of Warcraft version 4.0 anyone?
Patch 3.1 brings us Ulduar, dual specs, significant changes to all the classes, and more! We've got you covered from top to bottom with our Guide to Patch 3.1.