I don't know if I should revive an old thread such as I am now, though it's relevant!
Since Era was mentioned to be a playerworld that should be watched, it has finally been released! I think it's a success.
I want to add Shangri-La and Zodiac to the list, those two playerworlds seem quite good.
Aeon seems interesting, maybe the playerworld that has the most potential of being released as it has three worlds into one playerworld, which will be interesting. It would be cool to see it linked somehow, with quests where you have to travel the worlds or so.
Zenkou seems active a bit, it has a lot of potential, Haro41 and Zeon need to work on it hard so it'll be released!
Other people have playerworlds to add to the list?