Re: deleting empty groups. It's almost guaranteed to be possible, and I agree it would make sense. But that would mean more messing with lua, which makes my skin crawl. I already learned enough new reasons to hate it that will give me nightmares for a while.
(I exaggerate here of course, but this is a cosmetic feature, empty group doesn't break anything and it's just one click to delete if. It's unlikely I'll try myself in the near future. Unless someone is bothered enough by it to create PR).