I have three suggestions:

I wish there was some kind of favorites functionality. Nothing fancy, just a system tag for favorites, a quick-add button for said tag the right-click menu, and maybe a star on the thumbnails.

The current workflow for importing large queries (artists) is shit. Subscriptions aren't for large imports, but if you want to grab an artists stuff you're going to need one. So you have to manually do a run with the importer and manually make an identical subscription. I'd like to be able to right-click on an import query and pick an option to just make it a subscription.

It would be nice if there was a way or preserve generic metadata. I am thinking specifically of descriptions on pages like FA or e621. Nothing huge, just text box basically where importers could dump whatever into.