For most of the microgyms out there that are running a group fitness model, that will be your biggest revenue stream.
Then (depending on the model), personal training should be the next largest part of the pie.
Throw in some nutrition + retail and that's pretty much the current day status quo.
HOWEVER...I think there is a new revenue stream that is already here for some of us...but most of you are probably naive to it....good thing you have me to lead you to the light.