> Hard to say.  It seems at least possible that there are Python users for 
> whom stdin being unbuffered (with -u) matters, so if there's any 
> reasonable way of avoiding changing this it should probably be considered.

It's not about changing it, stdin has always been buffered in py3k. My
original commit actually attempted to change it, and it failed (I hadn't
noticed it at first due to mis-testing on my part). The new patch is
about putting it back in buffered mode even with '-u'.