I think this is a backwards incompatible change and thus will be rejected.  Currently there's a guarantee that "wait_for" can throw a TimeoutError *only* when when you await it.

   fut = wait_for(something, 0)

   # some important code

   try:
       await fut
   except TimeoutError:
       # do something

With your PR merged, the above asyncio code would be broken, because asyncio users can guard with try..except only the await expression.