I discussed this a bit earlier from a non-technical perspective with discourse staff people. In Germany, many non-profit communities use chat systems as their only place for group communication. It is not easy to convince them that discourse is a much better solution for “high-quality” digital interaction.
With a bit more insights into the technical details I now would agree that it is really a very hard (>> costly) task to create a link between a signal group chat as the source and a discourse platform as the target for some kind of “automatic group communication mirror”. The better way is to directly convince people that a switch to discourse is the best alternative to signal/whatsapp etc etc. But for this we would need a bit more improvements on the “discourse mobile/android” front, as already discussed at