I think the best we could do is have None.__format__ be:

def __format__(self, fmt):
   return str(self).__format__(fmt)

Or its logical equivalent.

But this seems more like papering over a bug, instead of actually fixing a problem. My suggestion is to use:
"{!s}".format(None)
That is: if you want to format a string, then explicitly force the argument to be a string.

I don't think None should be special and be auto-converted to a string.