Another idea might be to randomly generate all the lineups in Expo for the first four waves at increasingly difficult power levels and then draw from pit/col for the most used lineups for the 5th Wave...so only drawing three lineups from pit and Coli at all. This would also avoid repetition of too many lines close to the meta which can be another problem as well in Expo.
Anyway it just seems like there are some ideas to play with. As players we have no idea if they have seriously entertained any idea at this point due to extremely limited information on forums, Facebook, messages.
Maybe they could actually tell the players what they have considered and had to throw out and ask us for ideas and we can help them. Maybe someone will come up with a good idea (and we would be doing it for free so what do they have to lose by being open and honest)