[@CaptainManbeard] You could always be a "silent" DM. While we control the parts of the stories, you could jump in when you've got the time and throw a wrench in our plans or appear as a "ghost" to guide/save/harm our characters depending on the situation. 

[@Guardian Angel Haruki] I've seen it done before with custom races (primarily D&D) and you could choose the original race as we'd know it OR create a variant of your own alongside a location/country etc for it. The player then would have the chance when they'd be the DM to take the other players to the location and create a story there. If the main DM would see that things...stalled, he would've just jumped in and "timeskip" to the next location of the new DM.