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.