There is Tauthon[0] that (they said) also backported several features in non-backwards compatibility breaking ways, but the last commit to the repo was from December. Perhaps after running it for 3-4 years (and faced hostility from some Python devs - i remember at some point being downvoted just for mentioning it on Reddit), the maintainer got tired of it?
might also be indicative of how many people yelling for a fork were actually willing to put in the time to maintain it or pay for it?
(most places i've worked at, when we do the calculations for the business it's much cheaper/less risky just to upgrade to python 3, rather than to support python 2 or switch languages)
[0] https://github.com/naftaliharris/tauthon