CGUs are cool and we would like to do more. The problem is that they are tricky and thier aren't a lot of Champions that would be a good fit for a CGU. A CGU basically just takes the Art and Theme of a Champion and then completely deletes the current kit. The design team then rebuilds a entirely new kit, from the ground up, based on the current art and theme. So for Asol we felt that the Space Dragon theme was cool and resonant but the kit wasn't doing it justice.
Completing deleting a kit and building a new one isn't something we want to take lightly so it would have to be a case where we think the upside is high enough to take a kit (however unpopular) that some players have played 100s of games on and delete it.
I think thier are still a couple champions that could fall into this category right now, but we would have to find something new that was a clear upgrade over what's on live. If it feels lateral to players it would be pretty bad, sentiment wise