Yes, you can do this without Argument Clinic, but Argument Clinic allows to hide the use of unstable private API and cumbersome code under macros and in generated files.

> That said, it would be great if someone were to work on building-out AC to support more interesting argument patterns like those in round().

The problem is not only in Argument Clinic (and the Argument Clinic part is mainly solved). The problem is that currently it is not possible to express the signature of int.__round__() (and dict.get(), and getattr()) in Python syntax, and the inspect module does not support any non-Python syntax for this either. Once we invent the way to express it, supporting it in Argument Clinic will be merely technical problem.