When Legion was first announced, there was some question of what, exactly, this expansion would entail. Warlords of Draenor only had two raid tiers, and really only one major content patch (6.1 didn't count.) The Burning Legion is such a huge part of the Warcraft mythos - so much the "big bad" of the universe - that the thought that we'd ever actually have our ultimate confrontation with them seemed unlikely - yes, even during an expansion literally called Legion.
Well, it's looking a hell of a lot more likely now.
Ever since Burning Crusade, when the story of how the Draenei fled Argus as the rest of their kin transformed into some of the Legion's most dangerous demons, the planet has seemed like a clear choice for a future expansion.
But today at Blizzcon, they announced that we will be going to Argus some time after 7.2 during the Legion expansion (I assume they didn't say 7.3 in case they wanted to do something similar to 7.1 between the Tomb of Sargeras raid and our journey to Argus.)
All this time, I had assumed that the Tomb of Sargeras would be the expansion's final raid, and that our ultimate victory would be stopping the invasion. But if we're going to Argus, I think we're likely to see a far more definitive conclusion to the expansion.
To quickly recap:
The Nighthold Raid, which doesn't launch until next year, is going to be the first real "tier" raid - Emerald Nightmare and Trial of Valor are basically intro raids in the vein of Mogu'shan Vaults and Highmaul. This will have us defeat Elisande as well as Gul'dan, and in fact there are some leaked videos online that tell you just how that raid will end.
The Tomb of Sargeras will come out in 7.2 - and in fact, that's the name of the 7.2 patch. This will be Legion's middle tier, with 9 bosses including some Naga, the reanimated Avatar of Sargeras (the one that Aegwynn defeated) and Kil'jaeden as the final boss (much like Heroic Ragnaros in the Firelands, it looks like we'll be fighting him from head to toe this time.)
So what does this all mean? Well, with Kil'jaeden already used as a boss (and Archimonde very unlikely to show up so soon after he was the final boss of Warlords of Draenor,) that really doesn't leave anyone to be Legion's final boss except for Sargeras himself.
How that would even work is sort of beyond me, though I've postulated that Illidan's grand sacrifice at the end of the expansion (kind of a theme for him) will be to take Sargeras into his body so that we can kill both of them.
But let's think about what this means:
The Burning Legion is probably, actually going to be defeated. It's possible they'll do some sort of Wrath of the Lich King ending where the Legion still exists in some form (like the Scourge,) but it will clearly no longer be the threat that it once was.
Blizzard does have places to go after this - the Old Gods remain a threat, and we now know about the Void Lords, their masters. They're also clearly not saying that Azshara is actually in the Tomb of Sargeras raid, and while basically anyone except the Old Gods would be a step down from the Legion in terms of threat, Azshara could probably headline her own expansion.
This does heavily imply that we will not be getting an entire expansion dedicated to Argus, though, which I'll be honest, kind of disappoints me (on the other hand, it would be hard to imagine that the planet retains much of its old identity after thousands and thousands of years serving as the Legion's headquarters. It's probably a lot of black earth and green fire everywhere.)
It is quite heartening to see that Blizzard is planning far ahead. The sum of details on post-7.2 stuff is really just "Argus," but the fact that we know what's going on with 7.2 and that there's already a very clear third tier in the works is very good.