You had me up until the slots.
The idea of strict modules without those is fully acheivable as a modest enhancement. You would have very good chances of selling that more broadly and getting somewhere with it. But slots is poising the good idea with a much less workable sidecar. It's not that slots would never be a good idea, but static typing is also a good idea in many cases. Lumping these 2 functions together fails at separation of functionality.
Focusing on just static definitions in imports is something that really has legs. Out of the gate, probably 1/2 of python projects could do this fairly easily. You get nothing remotely near that with the slots.