After fretting about the removal of two-handed Frost and wondering what the mechanics of the spec are going to look like once we're wielding the shards of Frostmourne, whose names I'm currently blanking on, I've kind of wound up just deciding to go back to Blood tanking as a main spec for my Death Knight. After a brief stint as Blood DPS in early Wrath (I think I took him on one or two Naxxramas alt runs way back then,) I started tanking (also in Blood, after experimenting with the other specs, which could also tank at the time.)
Blood had originally been conceived of as the "physical DPS" spec way back before even the Wrath beta, but over the course of Wrath, it became a popular tanking spec (though there were Frost tanks too. Unholy wasn't terribly popular for tanking) and in Cataclysm, when, frankly, sanity prevailed and one spec was declared the official tank spec (the insanity was fun, to be fair,) Blood's penchant for self-healing made it the clear choice for tanking, and ushered in the first real active-mitigation-focused tank spec.
So through Wrath and Cataclysm, my DK was a tank. Through Mists and Warlords, though, he's been DPS - I think largely because A: my main's already a tank, B: I found the massive Obliterates of two-handed Frost really satisfying and C: the value of tanks has, well, tanked. With the dearth of dungeon content in favor of LFR raiding, and in Mists, scenarios that were designed to be run by three dps (basically a dungeon group without the tank or healer,) the natural population for tanks had plummeted.
In WoW's early days, it seemed (and admittedly, I started tanking pretty early, so I've got a biased perspective) like about a fifth of the player population was tanks (and another fifth healers.) This worked out, because back then, raiding was something only a small elite would do (think Mythic raiding now - maybe mythic and heroic) and so the main content for people to run was dungeons.
But even raiding was a little friendlier to tanks then. In Naxx-25, we'd take three tanks at least, and sometimes have someone switch for fights with huge numbers of adds (Noth the Plaguebringer, mainly.) These days, raids use two tanks, regardless of the raid size. And of course, this does let the fights remain consistent between sizes (important with flex mode,) but it also means that at most, tanks make up a fifth of the raid, and can be as little as a fifteenth.
I do think that a lot of players are more wary these days of performing those non-DPS roles, and particularly tanking, because there's really no way for tanks to pool their efforts (well, outside of the legendary ring ability.) Dungeons, despite putting more individual responsibility on the sole tank, are a great place to learn how to do it (though hopefully you'll start early in the leveling process, when the dungeons are more forgiving.)
So ultimately, I really hope that Legion does follow through on the goal of making dungeons relevant throughout the expansion, and I really, really hope that we get an expanding dungeon list over time (it worries me a bit that there are only nine dungeons at launch. What happened to the days when we could get twelve or fifteen right out the gate?)
But beyond that, I hope that Blizzard finds a way to communicate some of the ideas behind tanking. Unlike DPS and healing, tanking's not quite as intuitive - your D&D group doesn't have a tank; the enemies just attack what the DM wants them to. The proving grounds don't so much teach you how to position enemies or use cooldowns as much as they test whether you already know how to do those things. And there really needs to be some instruction on how to do a damned taunt-swap before you can queue as a tank for LFR. Seriously, I've run into so many co-tanks who either taunt back to make sure the boss is always on them while they stack up some deadly debuff or need to be prompted every single time I need them to taunt off of me. It's kind of a pet peeve at this point.
So I have high hopes for my Death Knight, wielding his Maw of the Damned (though he'll of course have the Frost swords for his offspec) in Legion. I just hope that this finest and most heroic of group roles will return to the noble position it once held.