The initial compiler will compile into C or use LLVM for the back end
This is .. a rather fundamental point. More critically, there is no link that I could see to any code.
It is an interesting idea, but it seems a little too under-cooked to merit much discussion right now. However, one way that this could get really good traction is if it were to support Cython code (which doesn't seem to be the case, from the FAQ)
Access to Python libs
Mypy will support accessing Python modules from mypy programs, running in the stock CPython virtual machine for the best compatibility. You can also access your existing Python code.
This would actually be even more compelling that I initially thought, since you pointed out that mypy run in stock CPython (I overlooked that and assumed it would have separate interpreter). All hypothetical, of course -- where's the github link?