They could always release the user created content in limits for each month, so in January they review a bunch of mods, check out the quality ones and make sure they work and if they are balanced and work properly they contact the mod creators and ask for their permission to include it as official content and give them credits for it then they release the top 10. When February rolls around they review another selection of quality mods and update the rooster of what mods to include in the next patch.
I do agree that allowing just any user created content is a bad idea, but limiting it, reviewing it and only allowing the balanced and polished quality content could work. It would also give modders a chance to get their stuff included in a game which would be great for their merits and since more is at stake they could be more careful to polish their content to make sure it works and is balanced.
Hell, for the next ES game (not Online) they should have a bunch of locked dungeons (say 50?) and then announce to the users after the game has been released that the 50 most well designed dungeons made by the fans will be patched into the game (assuming of course that the modders are okay with them using their content of course). So instead of Bethesda focusing on creating 230590 dungeons which mostly turn out to be copy pasta's it would allow them more time to polish up a smaller amount of quality dungeons and then allow the fans the chance to produce their own quality dungeons. (And no, it does not mean Bethesda is 'holding back content', it simply means they focus on quality over quantity and allow fans the ability to make some official content for free for other users.)
One could always just download mods but the quality of a mod is questionable, if it is developer-approved it could ease my worries a little. I downloaded A World Of Pain for FNV and that mod decided to crash my game constantly so I had to remove it. Since then I've had trust issues with mods.