Guido, do you have any thoughts on this?

Several of us (me included) think http://hg.python.org/lookup/c0d25de5919e probably should not have been done.  Mutating non-heap types crosses an implicit boundary that we've long resisted crossing because it opens a can worms and has potential to violate our expectations about how the language works.

[Mark Shannon]
> Breaking the interpreter in order to facilitate some obscure use case is unacceptable.

[Marc-Andre Lemburg]
I agree with Mark. This feature opens up a security hole large enough to drive a train through.

[Benjamin Peterson]
Probably the patch on that bug should be reverted.
  
[Larry Hastings]
As Python 3.5 Release Manager, my official statement is: Eek!