It's no secret that Morrowind is my favorite Elder Scrolls game of all time, and so I very much hope that this Reddit thread, which claims to have datamined a map of Vvardenfell in The Elder Scrolls Online, isn't some sort of hoax. What it teases isn't exactly the land of Dunmer and the Tribunal as it was—there are no Imperial outposts, for one thing, because the island isn't an Imperial colony during the time of TESO—but it comes awfully close.
The poster claims to have found "a ton of new tilesets" for Redoran, Telvanni, and Hlaalu towns, Vivec (the city, not the God-King), Dunmer strongholds, and Dwemer ruins. Seyda Neen, the town where Morrowind begins, is also in there, and apparently uses custom assets that make it look exactly as it did in 2002. Red Mountain appears to be inaccessible, and the foreign quarter in Vivec, the largest city on the island, isn't there either. (Which, like the absence of Imperial castles, makes sense: The Elder Scrolls Online predates Morrowind by roughly 1000 years.)
But there will also be new places to explore, including Redoran and Hlaalu towns, one near the Andasreth stronghold and the other close to Caldera, that weren't present in Morrowind. Based on the development maps, it will also be the largest PvE zone in the game, even with Red Mountain cordoned off—possibly close to twice the size of the Wrothgar zone.
It's all unverified, but as VG247 points out, it's awfully detailed for a hoax. Also relevant is that May 1 will mark Morrowind's 15th anniversary, and given that it's the game that really pushed The Elder Scrolls series into the gaming mainstream, I'd be truly surprised if Bethesda didn't do something to celebrate. Giving players a chance to return to return to Vvardenfell, even centuries prior to the Septim Dynasty, would serve the purpose nicely.