That's cool if there's any indication that this could actually be used in production. Namely, what is the compatibility with the ecosystem. The history of Python could be aptly characterized as a series of big problems -> tools promising miraculous solutions -> tools utterly failing to deliver on those solutions because they failed to consider some important part of the ecosystem. We need more than a benchmark graph to suggest that this is a panacea to Python's longstanding performance problems.

Mypy itself uses this extensively; it was developed because typechecking itself was getting too slow. So it’s seen some practical real-world use. It’s not a panacea (heck, it’s barely documented) but it’s an appealing option if you have some clear hotspot in Python that you need to optimize.

There is a very similar tool called Cython that is used by scikitlearn. Coincidentally Cython also solves a lot of python 2/3 problems since it compiles for both.