3series takumi, that was exactly what I was thinking about when considering a PN-S03 motor mod, but since I haven't pulled the mini-x motor can apart, I'm not sure if it's even feasible to somehow keep the armature but change the rod/motor shaft.
As for the thread, it's under 'shaft mod' the person who did it even has some pics so you can see what it looks like. Would allow you to use a 180 motor, or as large a motor as you're crazy enough to try to fit
How about an all-motor 540 mini-x!
Wouldn't even have place for the batteries almost
Of course though, if you take the time to do a mod like that, you could probably just go ahead and use one of NML's 30+mph mini-z motors. Should think that would be fast enough.
Sure would be nice to figure out how to just change the rod in the motors though. Would make for some nice mod possibilities, and still keep it LOOKING stock.