Have you checked out MyPy and the optional type hinting? I've been going that route in my python recently and been liking the both/and of having an optional type checker.
I have, and I do like that Python is heading in this direction. But this feature does still feel half-baked to me, the error messages are often confusing and I do recall running into a few bugs along the way. I'm also not certain that the type hinting will ever be 100%, the dynamic nature of Python seems to prevent that. This could end up giving some people a false sense of correctness.
The _getting started_ part could certainly be a bit smoother, I have had a few issues as well. Generally speaking I think for in-house things you can probably alleviate a bit of the possible dynamic issues that you mention - just by discouraging too much meta-ness.