Feeder league - have high school (and maybe college) leagues that run in the background. Players have amateur stats from actual OOTP simulation for the draft.
OOTP Generated - Like we've always done in the WBA, these guys are generated by the game just for the draft when the draft pool is created.
Reserve rosters - Each club has a reserve roster that doesn't play any games. Players develop as usual but don't generate any minor league stats. There aren't multiple levels, etc.
Minors - Like we've always done in the WBA.