Chances are exceedingly good that Arch package maintainers will be checking their Python applications and updating them to use /usr/bin/python2 if they don't run under Python 3. Actually, this should have already happened since the change has apparently been in testing for awhile.
I'm not really familiar with what Arch package maintainers do but aren't package maintainer mainly packager and not coders ?
I imagine that someone could easily be packaging 10 Python apps or libraries. He can't be upgrading all that code to Python 3 as it is not always a trivial task and would require a lot of work and constant patching if the developing team keeps working with Python 2.X
But overall, I think this is a good way to push developers to upgrade or at least prepare more to move to Python 3.
You're misunderstanding. Arch is still shipping Python 2.7 with the python2 package.
So package maintainers don't need to rewrite upstream code if it's not compatible with Python 3; they just need to update dependencies and set paths to point to the /usr/bin/python2 binary.
