What problem does this feature solve?

Here is a utility helper I like to use

export function useLocalModel ({ props, emit }, propName) {
  return computed({
    get () {
      return props[propName];
    },
    set (val) {
      emit(`update:${propName}`, val);
    },
  });
}

Here, the dependency injection is cumbersome / no conventions + no standard (should the argument be the first one ? the last one ?)

What does the proposed API look like?

Thinking about it, I came up with an elegant solution, that I don't think would be super difficult to implement:
Introduce a new built-in useContext composition function that would allow users to get the current setup function context (props, attrs, emit, slots).
Here it will make this composition a lot more clean and simple:

import { useContext } from 'vue'
export function useLocalModel (propName) {
  const { props, emit } = useContext()
  return computed({
    get () {
      return props[propName];
    },
    set (val) {
      emit(`update:${propName}`, val);
    },
  });
}

This is probably too simple to raise a RFCs but if there is a need, feel free to ask.
Regards.