Yes, that's true. And aren't some versions of RedHat still on 2.7 too? But I class this as a packaging issue more than a 2.7 vs 3.x issue: you see the same pro

Yes, that's true. And aren't some versions of RedHat still on 2.7 too? But I class this as a packaging issue more than a 2.7 vs 3.x issue: you see the same problems with (as a random example...) different versions of OpenCV - people not using virtual environments have problems even if they are all on 3.7. When I think of the "2.x vs 3.x problems" I was thinking more of the language and core libray level incompatibilities.