- The pure python repl started off in PyPy, although a lot of work was done to make it ready for prime time by the COython core devs - The lessons from HPy are slowly making their way into CPython, see https://github.com/py-ni - There were many fruitful interactions in fixing subtle bugs in CPython that stemmed from testing the stdlib on an alternative implementation

And more

Almost none of it will have been ported to CPython, as it's a completely different approach.