I got the idea for an AU called DELTALUNAR, where Kris and Noelle are adults and go to the dark world. All the dark worlds are more "advanced" than they were before:
Cyber World becomes Neo World, and it is a Japanese-themed giant city.
Card Kingdom becomes The Royal Throne, where it is hardcore medieval.

It would be very cool if someone could make things for this AU, and it would be very delightful to see this idea come to life!