As a maintainer of a WSGI application framework, I’m not clear how this proposal would work. There’s no standard for how to run a WSGI server, or how a WSGI application callable is prepared, so I’m not clear what sort of script you expect to be generated by installers. (This all applies to ASGI too.)
If you just mean that you want a standard way to specify “this is the WSGI callable provided by this wheel” you’d be missing the fact that a factory function is often used to generate the actual WSGI callable along with extra configuration arguments, which could not be described by an entry point alone.
If you need a replacement for the old setuptools concept of scripts, then using the modern project.scripts would be appropriate without any new spec.