mirabilos was referring to Alexander's reference to RFCs that advise against using 'Z'.  RFC are standards once they become formally accepted as such, and often they become de-facto standards before formal acceptance.  

Given that the method is supposedly conforming to a specific standard, it ought to do so...but in addition to the ISO standard there are other de-jure and de-facto standards and deviations to contend with.  Concrete examples are required for decision, I think, if the base standard is ambiguous.  It may be that a new method or a flag controlling the behavior needs to be introduced in order to satisfy specific wide-spread use cases, but those use cases need to be enough motivation to support such an enhancement.  By my reading, so far there have been no such concrete wide spread use cases brought forward to motivate any change other than deprecating utcnow.  ('now' must return naive datetimes to preserve backward compatibility.  If you don't want to use naive datetimes, make sure you don't...the datetime module was originally directly supported only naive datetimes (timezone is recent), so some care is needed.)