Next ESO expansion is (west) Skyrim. I am meh about this, as a location. Obviously there'll be a lot of cashing in on Skyrim, but between Bethesda itself and Zenimax I'm not sure anyone there seems to know how to handle Nord lore well. Not to mention Eastmarch and The Rift are two of the most boring zones in the base game, only beaten out by the endless trees of Valenwood for tedium.
What really worries me is how they're going to fuck up the Reach, however. If it is included in this area, which I actually hope it won't be. The Reachmen have been one-dimensional villains for pretty much all of northern Tamriel, appearing as antagonists in: Glenumbra, Bangkorai, The Rift, Orsinium and the Horns of the Reach dungeons. Also implied as being major dicks in Craglorn, given what the ancient Nedes from whom the Reachmen descend did to the Iron Orcs. And of course it was the Longhouse Emperors who helped start the whole mess in the Empire, with legalising daedra worship and invading High Rock and all. In all of this, while there have been tidbits of interesting lore, mostly we haven't learned anything since Skyrim. Reachmen bad, wear stupid fur armours, practice necromancy, worship daedra, oooh, bad.
Markarth is allegedly under the rule of a Reachman King, called the Tyrant of Markarth. However, any ideas that perhaps this King isn't so bad, and the reason there are so many Reachmen raiders attacking apparently everything in northern Tamriel because they have been exiled or something is rather undercut by the Tyrant aligning himself with Mannimarco's Worm Cult and hosting Abnur and Javid Tharn in the past. Best to leave the Reach as a separate DLC...that way if it does get fucked up, it won't be because of a divided focus between that area and Nord culture, such as it is.
One bit of datamining suggests there might be a vampire DLC in the future, with "Nightfall Crown Crates" being a thing. If so, I'm wondering if we're going to see some Volikhar vampires again. The Dawnguard clearly exist in this era, as evidenced by the Fighters Guild "Silver Bolts" ability. Yet...no Fort Dawnguard in the Rift. No Volikhar themed enemies in Skyrim at all. And the vampire tree could use a bit of an update, like werewolves got a while back. It's basically stupidly powerful passives and nothing else at this point...not to mention people would pay (actual money, no less) for the ability to not look like an ugly rotting corpse while still being a vampire. Hey, Serana was rather pretty for a vampire, wasn't she? And she was interred in that crypt at a point when Cyrodiil was not the seat of an empire...