Im not a huge modder, but my wish list is pretty simple really:

A base game that requires less mods to be simply playable. I.e. out of my 50 mods, Id say a good 20 of them are just vanilla improvements or gap fillers. I.E. I have a map mod that more clearly draws the roads and erases the stupid clouds so you can use the map like a map. I also have a mod whose sole function for me (though it does a lot more) is whistling for my horse. I have another mod that allows me to wear more than one ring. I have a mod so that I can have bags. Etc.

If we had a better base game, the modding community could focus on creating content rather than fixing vanilla issues.

And yes, bethesda, it would be super if you could keep an eye towards mod developers during your own development.