Signal should place someone who is somewhat technical between the customers of Signal and the development team. Many companies do this and it ensures that the person handling communication with the public has the time and energy to do so. I don't think this would materially change any outcomes but a couple messages to passionate customers along the lines of "everything you say is super interesting and I am listening, we as a company value your feedback" could go a long way.
And, of course, someone who is a bit more diplomatic may have better luck getting some of these issues across to the development team in an impartial manner.
Why is the lead Signal developer responding to the public on GitHub and Twitter? It is really helping the project? At this point I'd argue that it's actually hurting the project as we see more of these pointless and public flame wars. Others have pointed out the similarity between this situation and the IME keyboard kerfuffle a couple weeks back.