Hi Julien and welcome,

> - is this issue still open and needed ?

Yes and "perhaps". I have no opinion on whether it is necessary, but other people seem to think it's useful.

> - if yes, do I have to work from 3.3 branch, as stated in the issue "Versions" field, or in the default one ?

No, you should work with the default branch. Other branches only receive bug fixes, not improvements such as this.

If you haven't yet done so, you may also take a look at the devguide:
https://docs.python.org/devguide/