A change like this IMHO needs a migration path that allows for deploying to older Python versions, for example by providing a library/header that extension authors can use to port their code to the new API whilst still allow deployment to previous versions.
If such a convenience is not provided a lot of extensions will only be able to migrate to the new API when they drop support for the oldest Python version that does not support the new API.
That said, designing this can wait for later and should preferably not limit the design of the new API.
A change like this IMHO needs a migration path that allows for deploying to older Python versions, for example by providing a library/header that extension authors can use to port their code to the new API whilst still allow deployment to previous versions.
If such a convenience is not provided a lot of extensions will only be able to migrate to the new API when they drop support for the oldest Python version that does not support the new API.
That said, designing this can wait for later and should preferably not limit the design of the new API.