For me it's cosmic characters. Ever since reading Infinity Gauntlet and Silver Surfer as a kid I've always been fascinated with the cosmic characters. A whole wave dedicated to cosmic characters would be insane but they'd never do it because alot of those characters are pretty obscure. Here's what I'd like to see in my fantasy cosmic wave.
Cosmic Spiderman (because they'd make me include a Spiderman,Wolverine or Iron Man)
Celestials (running changes)
Living Tribunal (BAF)