Forgive me if this has been done before, but I haven't seen it. I don't have the time to run a new progressive league (or even join one), but I wanted to throw this suggestion out there.
There are two general types of progressive leagues.
(1) A single-season 24-team league where the talent pool is very thin and you can get teams winning and/or losing 120+ games. It's really hard to replace badly managed teams.
(2) Or a league where you are combining two (or even three) seasons so you have guys from 1910 playing with guys from 1990 or whatever. The talent pool is better but mixing eras sometimes gives odd results. Sosa isn't going to hit 60 HRs facing Mathewson, Walsh, W.Johnson, etc.
I came up with a way to resolve both issues.
Pick a season to start, it doesn't matter (let's use 1920). Then hold a player draft as usual. The difference is this progressive league uses 2 successive years as it's player pool. The owner gets to choose which season to use. So, if you got first pick, you could choose to use 1920 or 1921 Ruth. Nobody else would get Ruth. The following season would use players from 1922-23 and the Ruth owner could choose either 1922 or 1923. Every WIS-season would advance by 2-year increments. If a player played only one of those seasons, you'd have to take that season (way fewer players on IR).
The beauty of this concept is that is opens up the talent pool for 24-team leagues while keeping the stats somewhat consistent. There's more opportunity for bad teams to get better, because the talent pool is better. Of course, you progress through a player's career twice as fast, but that's not necessarily a bad thing.
Anyway, just wanted to throw this out there in case somebody wants to run with it.