Thanks for wanting to contribute.  However, I don't see why this function would be beneficial.  As indicated by the patch, it is simply

  ''.join(str(map_function(x)) for x in iterable)

but without the inherent flexibility of the above formulation.  Which looks pretty Pythonic to my eyes :).

We often say "not every one line expression deserves to be a function."

But yes, python-ideas would be the appropriate forum to discuss such a thing.  This issue can be reopened if you get consensus that it is a valuable addition.