And yet even the best mods, which often take so long to make that most people will never even hear about them, still don't compare to professionally designed DLC or expansions. Sorry, they just don't. And I also don't see the implied value in waiting a decade for a mod that would even come close to that level.
Despite your number of posts, this makes me think that you're not familiar with the mod community. There were a lot of mods out for Morrowind and Oblivion that were clearly as good or better than the content BGS puts out (though generally on a smaller scale, aside from some exceptions like Nehrim). Actually I can name a few where the modder was apparently more skilled than the folks at BGS. (Not trying to disrespect BGS, but there are very talented people out there doing mods, and they're not limited by deadlines).
Just for Skyrim I'd point out SkyUI, Skyboost (a bit of an embarrassment to BGS), Duke Patrick's combat (whose Oblivion work was diluted into Skyrim's archery), Weapon and Armor Fixes, UKSP, Wrye Bash/BOSS/NMM (makes Steam Workshop look like an embarrassment), several texture optimizers that improve the compression method used in BGS' own files, the list already goes on and on, and we're still relatively early in the modding scene.
A surprising number of Skyrim's features first appeared in mods that go as far back as Morrowind, and they were often more sophisticated than what we're seeing from BGS now.