One of the interesting things to be found in the datamined abilities coming through the first Legion Beta build (note: the Beta hasn't actually begun, but the information is now on the servers to be downloaded) is that it looks like all longterm buffs are gone. That's a whole slew of things, and it's a bit of a shock, as buffs have been around for WoW's entire lifespan. It's a slaughtered sacred cow, assuming that it's really true.
Evidence in favor of the disappearance of buffs certainly comes in the form of new Paladin Blessings, which are short-term effects akin to the existing Hand spells. For those of you who remember way back in the day (I think pre-Wrath,) Paladins had a much larger number of Blessings. Some were your standard long-term buffs (though they had a shorter duration, only going for five minutes, but getting bumped up to 15 when you used a Greater Blessing, which consumed a reagent and blessed all members of the same class - the base versions had to be cast individually, like most buffs back then.) Because it was annoying to have, say, a Blessing of Protection overwrite a Blessing of Kings, they separated out the short-term and long-term ones into different kinds of abilities, creating the new Hand spells. But it looks like Salvation is becoming a Blessing again (actually, the original version was a long-term buff,) and there's no mention of Blessing of Might or Kings, or any other classic buff like Mark of the Wild or Power Word: Fortitude.
It's possible they're just going to shift to an aura system - Hunters have long provided the attack power buff of Trueshot Aura through a passive aura. But Trueshot is becoming more of a marksmanship cooldown that seems to do entirely different things.
So what's the gain, what's the loss here?
The good news is that your raid composition will be far more flexible. You don't need to make sure you cover every single buff (not that it's too hard these days,) and if you have a guild that happens to have a large number of, say, Unholy Death Knights, you're not missing out on anything by letting them all come instead of bringing a more diverse crew (well, you might be melee heavy.)
But of course one of the reasons for these buffs in the first place was to encourage diversity. While it's certainly not the way I play the game, a lot of people desperately want to maximize their power, switching specs or even classes to ensure they're pumping out the most DPS. A change like this could risk creating a situation in which the top raiding guilds (or anyone with delusions of being that hardcore) take whatever spec is doing the most DPS at the moment and no one else.
Still, this is pre-Beta, not even early-Beta, and this isn't set in stone by any stretch. Still, I'm curious to see what Blizzard might do, if anything, to keep raids diverse. Especially in an age of personal loot, there should be at least some incentive to do so.