I'd love to hear your suggestions for changes we could make while keeping it somewhat WSGI-compatible. It took a few years to refine it to where it is now, so it's not like we just threw something at the wall.
There's the problem. WSGI is fundamentally flawed too - it could also be using generators for a two-way communication channel instead of stringly typed callbacks.
In a world where Python has optional static type hints, it would be nice to have concrete objects passed too.
Can you expand on the stringly typed callbacks? Where are they required? Are you referring to string keys in a callback dictionary, in which case stringly-typed seems a bit of an odd choice of words.