It's easy to forget now, but there was actually what seemed like a pretty major talent revamp in Cataclysm.
Throughout Classic, Burning Crusade, and Wrath of the Lich King, there was no moment at which you explicitly chose a spec. Instead, each class had three talent trees. Every level starting at level 10, you'd get a single point to put into one of the many talents in these trees. Once you had put five into a tree, the second tier of talents would open up, another ten (though the second group of five did not have to go into the second tier of talents) would unlock the third, until about twenty levels below the cap, at which point you would have the final talent of the tree. Typically, you'd then start investing in some of the low-level talents of other trees.
The odd consequence of this was that until you got to level twenty or even thirty, there actually wasn't a huge difference between the various specs - an ostensibly Holy Paladin could easily tank a dungeon at that level.
Cataclysm added the idea that you would choose a spec at level 10 and instantly get a number of clear bonuses to really drive home the idea that you had chosen that specialization. Rather than very gradually orienting an Enhancement Shaman toward melee attacks, you immediately had Lava Lash and an ability that gave you spellpower based on your attack power.
They also locked you into a given spec - there were actually builds back in the day that put a relatively even number of points into multiple talent trees, but Cataclysm locked off the trees outside your spec until you had spent enough to have the final talent (though you didn't actually need to spend that last point on that final talent.)
Obviously, Mists of Pandaria's talent overhaul was far more dramatic, with the new system making Specialization and Talents completely different game mechanics.
In addition to the number squish we got for Warlords (something that I imagine most people don't even think about anymore. Remember when we were doing 300k DPS in Mists?) there was also an "ability squish" that seriously reduced the number of abilities clogging up action bars. Mostly, this was a good thing (I'm so glad that Mages don't have to mutli-dot with their bomb spells to AoE anymore and constantly use their mana-regeneration talents. Leave that to Warlocks!) But while I think they pushed things in the right direction, it was something of a half-measure, much as the Cataclysm talent revamp was.
There's nothing terribly specific, but at this Dragoncon, we started to hear about the idea of giving lots of specs new resources and even new names (the latter of these is the most mind-blowing.) Survival Hunters, we know, will be essentially a whole new spec, but I wonder how extensive these class changes will be.
Major class changes can be a big risk, and I've certainly had my disappointments in this department (Arms Warriors. Never Forget.) But on the other hand, perhaps some serious re-working could result in much more interesting specs. In Cataclysm, all three Warlocks specs played pretty similarly, but the tear-it-down, build-it-up approach they took to revamping the class resulted in some really cool gameplay (at least for Demo,) and also, even though this isn't really the most important thing in the world, some cool-looking elements added to the UI.
Taking Arms Warriors as an example, the revamp in Warlords was meant to focus the spec more on making those massive Mortal Strike hits. But in order to do that, they had to remove a lot of smaller sources of damage, like Overpower. If Blizzard were to go so far as to create a whole different resource system for Arms (Rage always seemed more appropriate for Fury,) they might be able to custom-design it to ensure that Arms got compelling gameplay instead of the current model of "auto-attack until you have enough Rage."
I've been lamenting the death of two-handed Frost and begrudgingly forcing myself to play DW Frost for the remainder of Warlords to prepare myself, but it's possible that this is foolish, because for all we know, the spec might be getting overhauled with a totally different rotation.
Blizzard does need to tread lightly here, though. As someone who plays a Paladin as a main, I remember the transition in Cataclysm to Holy Power. Ultimately I think it was a good move for the class and prefer the way Protection plays now over pretty much any earlier iteration of the spec, but not all these changes are going to be big hits (and there are still people who want to get rid of Holy Power these days for some reason.) Rotations do naturally have to change somewhat over time - some Rogue specs essentially play the same way they have since vanilla - but sudden, jarring changes have to be managed carefully. And doing this to every spec, or even most specs, could really cause a cascade of discontent - even if those changes actually improve the gameplay of those specs.
As someone who doesn't really play a Survival Hunter, it's easy for me to sit back and think its cool that Hunters are getting a melee spec. But if they turned around and made Protection Paladins into a healing spec, you can be sure I'd be grabbing my torch and pitchfork and driving down to Orange County.
Here's looking at Blizzcon, and hopefully imminently thereafter, the Legion beta.