LoreRim is one of the biggest modlists for Skyrim, and after playing it for a week, I think it might be the best one, too.
Falskaar is a particularly famous mod. It is more of an expansion pack than a simple questline ... you from various sources. Who needs Skyrim: Special Edition, eh?
Elsewhere, the "HD 2K Texture" mod pack is a high-resolution addition ... While it remains to be seen if it'll pass Skyrim Special Edition, one thing is clear: don't doubt Skyrim's lasting popularity.
Skyblivion itself will be free, though TESRenewal said you'll have to own Skyrim: Special Edition, Oblivion, and all of Oblivion's DLC for the Skyblivion installer to work. Oblivion and its DLC ...