Is there any info on whether you can use Nexus mods on the Steam machine coming in the Fall? Nexus seems to so far have better quality mods.

If you're talking about the Steam Machines I think you are, they're Linux computers, so you can't run Skyrim on them anyway, unless it's through WINE or something. In which case, if you can run Skyrim, I can't see any reason why you wouldn't be able to use mods from the Nexus.