Just rip the band-aid off. Some of the async stuff in Python 3 is awesome. A bit curious that 3.4 has been dropped, as that's the stock Python 3 shipped for CentOS 7.
The code I've written recently relies heavily on async and data classes, both of which are recent additions. I can't imagine choosing Python 2 at this point.
I'm really upset at the distro vendors, they should have upgraded their base system Python scripts to 3.x years ago and just included 2.7 for legacy support. RHEL 7.0 came out in 2014 for goodness sake.