Here's a couple of progressive ideas I've had kicking around for a while. I would join either but haven't had the time to commit to running any more of them.
PCL Progressive
You know, like the Pacific Coast League? The league starts some time around 1946, or maybe 1977 or even 1993, but the idea would be to recreate the feel of the PCL in the 40s when it was almost another 'major league.'
It would be a 16 or a 24-team league. One half of the league is the "major leagues" and functions like a perfectly normal progressive. The other half is the PCL and functions entirely with AAA players. PCL teams would all use west-coast ballparks and major league teams would use east-coast ballparks.
Not sure what quality of AAA players would work best - initially I was thinking Way Above Average, but those teams would probably be a bit better than the progressive side. Unless we started later than 1946, and then the progressive side could have 12 teams and be pretty deep. Above average would definitely be worse. I hate Random, there would be way too much luck involved (but hey, other people can take this idea and go that way if they want).
The PCL teams would not participate in the progressive draft but they could trade for picks, players, whatever. In other words, Joe Dimaggio could go over to the PCL. And if you allow renaming your AAA guys, then you could give them the same names every year. Buzz Arlett could finally get his chance.
There's still a lot more thought that would have to go into the setup but I think it could be really fun.
The superstar progressive
This would be simpler. It's a standard progressive, you start in 1969 or 1977 or 1993 or whatever, and either have a draft or have people pick franchises and keep a few players. The usual ways to start a progressive.
The only catch is, everyone gets one superstar player from a bygone era, and that player progresses normally along with your team. So you might have Ty Cobb, and if the league started in 1977, he would start in 1905. When you went to 1978, he'd be in 1906. Obviously it would be better if you couldn't trade away your superstar. And maybe Ruth would have to be blacklisted. There could be a new superstar draft every 20 years, so if you pick someone with <20 years, you'd have a few years without a superstar.