When it's only a matter of style, as here, then yes, I think we can take that question to the list.

Technically speaking, however, having looked at this problem a fair bit, at a minimum, the examples need to remain valid Python 2 in the source.  (Until we stop supporting Python 2 altogether).  The ultimate solution here is probably going to be 2to3'ing the doctests to make them run on Python 3, and possibly displaying the code as Python 3 in the browser through some sort of user configuration (i.e. there would be a drop down at the top of the page to display the examples in Python 2 or 3).  Given that 2to3 exists, we can do this.  Since 3to2 doesn't exist, we wouldn't stand a chance going the other way.