We didn't try numba and couldn't get pypy working; we had dependencies that didn't work with Pypy. I'm curious about numba though.

I don't think well written cython should be any more unmaintainable than Go IMHO.

I've written a lot of Go, it's always struck me as about as maintainable as Python (I would put it at a bit more maintainable than Python given its mature static typing story--mypy still has lots of problems). I haven't given Cython a fair shake, but it doesn't seem very well-invested in; this is generally what has kept me away from it.