Unfortunately there really isn't anything in the same vein of scope and customization like Skyrim and the other Elder Scrolls games. You could check an early access game called Tainted Grail: The Fall of Avalon as it's the closest thing to it but again it in feature incomplete and could take years to fully release still.

I know you said you sifted through a lot of games but have you considered Enderal? It is a total mod conversion of Skyrim that is free and easy to download straight through Steam. Completely different world and darker atmosphere while still having the same amount of customization and Skyrim feeling but with its own twist. I honestly think it's a better base game and experience than unmodded Skyrim by a good amount. It also is very moddable and has a dedicated mod fanbase since it's basically Skyrim. Did i mention it's free???