Rule to allow for endless floors with perhaps additional rules or challenges added per floor

Exmaple:
Floor 1 ~ 3 normal
Floor 4 ~6 Increase monster health
Floor 7 ~ 9 Increase monster damage, add player cards
Floor 10 ~ 12

This is possible, however it would be Skirmish only. I've tried going beyond the 5th map in multiplayer and it just doesn't work for the clients. They hang in space because their client doesn't think it's allowed.