Re: Freedom-verse game w/ growth? (M&M 2nd ed)
I think with a clearly defined progression timeline it could be a fun way to play.
By that I mean everyone knows and agreed that you'll, for example, play through a story arc with everyone at Power Level X as new students at the academy, then you'll bump both the time and the character's mechanics up to experienced students and go through a story there. The next bump might be when the characters have graduated and are starting to establish a name for themselves, then when they make it onto their first team, etc, etc.
I think the key thing would be having everyone on the same page at the beginning and a clear plan for how the game itself will progress. If you try to play it more traditional with smaller jumps in time or very day to day progression, with the PbP format I don't think it would work as well.