I agree that it is a tolerance varying widely from person to person.
I play 35" fivers down to 30" shorties with no problem. Then again, I play just about anything with strings on it, from the tiny soprano uke to the 4/4 double bass, and all points in between, guitar, banjo, mandolin, a little violin, et. al. So quickly adapting to different scales and neck dimensions is part of the deal.
I will say that if you are a guitar player, going from a long or standard scale bass to a 32" or 30" immediately feels really fast and easy. I think the adjustment is less about technique, more about conserving motion. I believe most players, short of physical issues, could vacillate between electric bass scales fairly easy with only a little determination. And that ability opens up a whole new world of some pretty amazing instruments.