If it were up to me, I'd have DC release a bunch of $1.00 Issue #0's for each major character/franchise told from the perspective of some omniscient observer like Metron or Rip Hunter or something. (If there's a new crossover event being planned, they can be relating it to a Guardian of the Universe or the next Big Bad who wants to study Earth's heroes for some reason). Decide what aspects of their Greatest Hits you want to mishmash together, what relationships you want to emphasize, and tie it into a narrative of what makes the character special. It would probably require a good deal of planning as the next creative team will have to help lay the foundation for what they want going forward. But it would generate a lot of buzz, satisfy a lot of fan questions, and give the DCU a more concrete sense of place and time with these characters that is badly needed.