> While it regularly publishes the code of its client apps, it hasn't updated the Github repository for its server for almost a year.

Last commit was 5 days ago: [0]

As for not playing nice with third-party clients, I can give you that point.

[0] https://github.com/signalapp/Signal-Server/commit/365ad3a4f8...

It's practically a principle of the Signal project to discourage third-party clients. Signal's security work is done, for obvious reasons, mostly clientside. If you have a diversity of clients, you're stuck with the lowest common denominator of mainstream clients. Without them, you can roll out any feature you want to.

> It's practically a principle of the Signal project to discourage third-party clients

It depends on what you call "client". At the protocol level sure, you're supposed to behave just like any official client. But to do that you just have to use their client library[0] and implement whatever you want on top of this, like signal-cli[1] has been doing successfully for quite some time now.

Some forks exist here and there (from memory, there's one with WhatsApp import, another with UI features), there's just no interest for a completely new client. There's only so much space for innovation for what is mostly a messaging app.

To be fair, the absence of an API (which Telegram has) also limits possibilities.

[0]: https://github.com/signalapp/libsignal-client [1]: https://github.com/AsamK/signal-cli