If any leak could be described as "big if true," it's this one. Fans of The Elder Scrolls (so, like, everyone), rejoice. According to one Redditor who, understandably, doesn't want their identity known, The Elder Scrolls VI might see a 2025 release - although that is still completely up in the air - with many new and/or improved things compared to the previous titles. The game takes place in Hammerfell and High Rock and the main quest revolves mostly around the Direnni Tower and the evil Thalmor.
While the leak pinpoints the region of Tamriel where the game is supposed to take place, it doesn't mention much otherwise, except that the landmass seen in the trailer (released back in 2018) is actually Yokuda, the archipelago remnants of the Redguards' homeland. High Rock supposedly takes a lot of inspiration from concept work on Battlespire from back in the day. The setting apparently goes a bit further towards a mystic world, as magic will be key in solving the main quest.
Speaking of the main quest, it allegedly centers around the Direnni Tower, or the Adamantine Tower, that veteran TES players know from Daggerfall. Considered the oldest building in Tamriel (maybe even the entirety of Nirn), it is believed to have been built by the Aedra very soon after the creation of Mundus, or the realm of existence that encompasses Nirn, and is surrounded by Oblivion. With the Direnni Tower central to the plot, it is to be expected that we will get a lot of new lore about the entirety of the TES world. The storyline is about the Thalmor (the paramilitary elven force we've come to know, but not love, in Skyrim) trying to unravel creation itself.
In line with the magical questline, the magical abilities of your character are getting serious improvements, the leak continues. From new additions to schools such as Alteration, Conjuration, Restoration, and Illusion, over spellmaking, to levitation from Morrowind, the magic system will play a much bigger role in the game. Also continuing from Morrowind, vampire factions are supposedly back in the game, with different kinds and perks available. Last but not least, factions/guilds are also getting their share of improvements. The Thieves Guild, the Dark Brotherhood, and the Fighters Guild are all returning, while the Mages Guild is long gone, so the remaining mages are trying to reassemble and start a new academy.
With all of this said, the Reddit user still doesn't want to "spoil too much for you guys" because "discovering new things is part of the magic of Bethesda games." With what we know by now, the best part of the game will be comparing the leaks with reality once the game is out. But if the leak is true and we're still half a decade away from it, we'll probably already forget all of this by then.