I think the approach that might actually work for a PW would be to have limits on how many RPs are going on at the same time and set endings for them.

So if I launch "Streets of Gotham" as a Character RP to end in March 
Odin could launch "Justice League" to start right after, dealing with the events and changing the world.  That RP ends in May.
Promise begins "Tabula Rasa" set in the days leading to the end of "Justice League" and beyond, detailing that Raas Al Ghuul guy plotting how to turn all the Justice Leagues hard work to ash.

Each subsequent RP holds the events of prior RPs as canon, all characters (unless by mutual agreement) persist.