If the sport can't sustain 13 pro teams, how could it support two leagues of 10?
Can't sustain in its current format. There's no immediate increase in revenues coming - Attendances aren't going to suddenly swell, nor are TV deals going up. So the only option is to reduce costs in line with revenues; fewer games and a reduced cap.
If you can bring costs down in line with revenues, then you have sustainable clubs. It doesn't necessarily rely on crowd growth to work - although I think as a result of fewer games with more predictability of internationals playing you'll see a steady increase in matchday attendance.