I'm not sure how many franchises MLS is willing to expand to, but the limits of human stamina will be the limiting factor. If you structure the league so that every team plays every other team home and away, you can only expand the league so far before players simply can't complete a full season without breaking down. European football is already arguably crossing that threshold, so I don't really see the league going much beyond 22 teams...
...unless MLS does what the NFL does and only require teams to play other teams in their conference home and away, and then just a selection of the remaining teams. I would not like to see that. I want to see them get rid of the conference system altogether and go to a single table. I would also not be against the institution of an apertura/clausura system that would bring us more in line with the FIFA calendar.
As for promotion/relegation, IMO it's never going to happen in the US, there is just no culture for it here and the moneymen hate it. The only reason it still exists anywhere is tradition - if the business suits at top teams had their way in Europe they'd freeze the league system so the best teams stayed on top forever, with no fear of the drop. You know, that European "super league" idea. Basically turning the Champions League into a permanent Pan-Europe oligarchic league.
...unless MLS does what the NFL does and only require teams to play other teams in their conference home and away, and then just a selection of the remaining teams. I would not like to see that. I want to see them get rid of the conference system altogether and go to a single table. I would also not be against the institution of an apertura/clausura system that would bring us more in line with the FIFA calendar.
As for promotion/relegation, IMO it's never going to happen in the US, there is just no culture for it here and the moneymen hate it. The only reason it still exists anywhere is tradition - if the business suits at top teams had their way in Europe they'd freeze the league system so the best teams stayed on top forever, with no fear of the drop. You know, that European "super league" idea. Basically turning the Champions League into a permanent Pan-Europe oligarchic league.