Morrowind had (and still has) just as vibrant a modding community as ES4 or 5. Tamriel Rebuilt alone is still the largest modding project for any Elder Scrolls game.

All of that expertise was developed on and for Morrowind.

We don't have the SF version of the Creation Kit yet, but all previous versions are largely similar, and FO4 modders will likely have no issue working on SF.