Multi-speed fixed gear
I accept that this may be the dumbest thing that some of you have laid eyes on (though i doubt it considering some of the content on here), but I was just thinking about this...
Say such a thing existed as a fixed hub with a 9-speed cassette on it. Couldn't you theoretically have a multi-speed fixed gear? Does a derailleur need to be used with a freewheel or freehub to work?
I can't say I'd ever want such a device as it'd kind of be the worst of both worlds (no coasting, loss of simplicity of a SS drivetrain), but in theory could this work?