There will be no promotion and relegation.
However—if there could be—the major leagues could be dramatically expanded, to maybe 40 or more teams. There could be four levels of ten, or five levels of eight. With that number of teams, could be tables instead of divisions, with a truly balanced schedule.
One downside of this system is that, if done as in Europe, you might never see the best teams in baseball come to town if you are in a lower division. Well, how about this:
Adopt a point system, three points for a win against your own division. Play at least one series against every team in every other division. If you beat a team above your division you get an extra point per level for each of those wins added to your season total. Beat a team below your division, you get one fewer point per level.
So, say it’s a five-level system of eight teams each. You’re in level three. You get three pints for a win against your level. If you beat a level one (Premier League?) team, you get five points; level two, four; level four, two, and level five, one point.
This way, playing a team from another division would not be a “friendly”, sort of like in English football, but there would be a practical concession to the different levels of team ability.
I love noodling this kind of stuff.