I revisit Xonotic every once in a while but I've never stuck with it for long enough periods.. often I just play the singleplayer campaign against bots to blow off some steam and barely even get online.
I think what would make me stay in the game longer, personally, is less focus in competitivity and more in coop modes. I was pretty hyped when I heard about the plans for an invasion-type mode where you fight against monsters. I don't have the time or the dedication to get too deep into the competitive scene, but a no-pressure coop mode I could dig it.
Maybe there could be some doom-style maps that combine CTS with some enemy waves and that can be used as a tutorial level that's non-intrusive (as in, one that gives indications but doesn't force feed them to you so it's not tiresome to re-play), so that it can be fun to play in multiplayer coop too.