> This is Python3 as most of us wanted it to be.
> Valid Python2 is Grumpy already.
> It compiles existing Python2 AND offers a legitimate upgrade from CPython at the same time.
> As far as all of the lost C extensions? You won't need them
None of the statements are true. You seem to be very confused what Grumpy can and can't do, and what the need of actual Python developers are.
The only benefit of Grumpy is speed (I don't think go "interop" counts). Now, that's a pretty big benefit for some, but comes with significant drawbacks and probably always will. Even though CPython is only the reference implementation, many clever people have worked to make it faster. Getting rid of the GIL is also very difficult. The easiest way to gain speed is to limit Python to a subset of features and then optimise for that. While this is a fair approach, hailing it as the future of Python is terribly misguided.