If each change to the public interface in the Specification section
necessitates a new draft, is that too often? Of course an author can
batch many interface changes into the same draft.

I feel we're grappling with a very similar question as the inventor(s)
of semantic versioning (https://semver.org). The semver rule is:

- Increment major version when you make incompatible API changes.
- Increment minor version when you add functionality in a backwards
compatible manner.
- Increment patch version when you make backwards compatible bug fixes.

In semver terms, my suggestion would be that each major version requires
a new draft.