The hub motor I have gets very little use so I have no real idea what is going to happen to the motor itself.
On the currie 24v motor I use on my friction drive, I have run them as high as 48v for a mile or so but went back to 36. The thirty six with a heavy duty 24v controller runs fine and I have used it for my purposes with no problems yet. I think the motor would do 48 for a few miles with no real damage and they are replaceable for very little money.
Hubs are not cheap. Mine is a motor I care nothing about. If it melts down, then I would most likely be better off time wise, since I get this urge to screw around with it now and then and waste my time on it.
I have a 36v 500 watt controller on it now, so I have to run at least 36v through it. I doubt that this controller will run more.
The 48v test I did on the curry friction drive I built was a complete success, so one day I might spring for a complete set of four sla and put them on the big trailer and bike. It might even be my spring present to myself.
To be honest I wonder how a 36v lith powered motor would compare to a 48v sla powered motor. They might turn out to be similar.