> As a process comment: I agree with what Victor wrote in http://haypo-notes.readthedocs.io/pep_random.html#status-of-python-3-5-2, when he suggests that we leave 3.5.2 as is for now [...]

I agree in principle.  Certainly we all agree it'd be inappropriate to add the block parameter to 3.5.2.

I only allowed the possibility of adding os.getrandom() in 3.5.2 to try and placate the authors of cryptography libraries.  They could use os.getrandom() if it was available, and fall back to os.urandom() if not.  Since they want the blocking behavior, that means they'd block in 3.5.2+ (they'd call getrandom), and they'd also block in 3.5.[0-1] (they'd call os.urandom() which blocks on Linux in those versions).