I would say, focus on what makes your web framework different. i.e. if you want to implement py-to-js, don't also reinvent routing at the same time. Grab an existing py-to-js engine and make something tiny with it. If it shows the value of the idea, then it will be picked up by the wider community. I like the idea of decorators for turning query and body parameters into function parameters, I haven't seen that before…
The decorator for body params reminds me a bit of Spring's @RequestBody annotation. However, fastapi manages this without a decorator, only a type hint. Is there any gain doing it like this?
It's nice to have explicit demarcation whether the parameter is coming in from the query string or request body.