Add a download and link history page for users to see what they've downloaded or which mods they've looked at in the past.
More features that, realistically, are standard requirements for a modding site.
Features like NexusMods' download and file view histories would be great, so I can see mods I've used on previous installations or looked at in the past and didn't have the chance or required mods to install at the time.
The programmers mostly focus on NexusMods currently and don't really have the time for big changes/new features.
I don't see that happening anytime soon (if ever).