Well, it's solvable in the sense that breaking language compatibility is a choice that doesn't have to be made, I guess. The 2->3 transition was managed as effectively as such a big thing could be but it's for left the industry littered with a bunch of weird self-maintained python2 forks, compatibility layers for the C side of python. A 2x theoretical performance improvement doesn't pay down the engineering costs to make a switch if you recoup it in lower hardware costs later.