What are some of your favorite dream crossovers that you can think of? For example I think a big 07th Expansion crossover with all the characters in a story or visual novel of some kind would be neat. However feel free to expand outside of 07th Expansion / WTC if you wish.
My own personal pairings would be Ace Attorney and Detective Conan; I think would make an excellent crossover. Danganronpa and Umineko would make a swell pairing as well.
Don’t feel you need to limit it to just visual novels or even video games; feel free to let loose with your imagination, wishes, and desires.