Johannes Schauer's note of the 21st Dec 2017 said he was waiting for a new Dudle release; 1.3 was released not quite a fortnight later, Jan 3, 2018.
The extension packaging discussed here is apparently still to be done: https://github.com/kellerben/dudle/issues/82 I think, subject to correction, that this isn't blocking the inclusion of the main Dudle package in Debian, it would just make it awkward to incorporate the extensions. Is there anything I can help with here?