The Wikisource extension seems to work well in the beta cluster and there is a consensus in the French Wikisource community to deploy it on their wiki: https://fr.wikisource.org/wiki/Wikisource:Scriptorium/Novembre_2019#D%C3%A9ploiement_test_de_l'extension_%22Wikisource%22
It would be nice to deploy the extension first in frwikisource and then generalize it to all Wikisource is everything goes well.
The extension is already properly configured in make-wmf-branch/config.json and branches seems to be done properly.