Brave and the Bold movie team ups.
The Brave and Bold movies could be used to introduce the characters, team up characters that have been in movies with those that haven't to help establish them and launch their franchises.
Batman, Superman, GL, have had their own movies and most people know about them now. Wonder Woman had a successful TV series, and that might help. But maybe not. Those with movies would help those without and launch those solo movies that have been a long time coming.
It would depend on the story, but I would like to see Superman and Martian Manhunter. Because they are both the last of their kind, the only survivors, and both incredibly powerful. But Superman looks human so he is more accepted and free on Earth than Jonn is.
I'd like to see Flash and GL. A Crime Scene Investigator and a Space Cop.
I'd like to see GL and GA, like the Neal Adams run, a space cop and a robin hood radical.
Batman and Wonder Woman might be fun, show a developing love interest like in the comics.