Mypyc is stable for what it supports. Mypy itself is built with it. Black is built with it. I use it in production for some things, but use Nuitka for others. That decision is mostly down to a project's dependencies, not the project's own code. The more magic a Python module has, the harder it is to build AOT.
e.g. PyPy doesn't work with PyTorch https://github.com/pytorch/pytorch/issues/17835