As long as the Signal desktop app is a 420 MB[1] pile of Electron, I refuse to install it. I may be a dinosaur, but a good desktop app is a requirement. I hate typing on a touch screen.
I am ok with Electron if it is needed for Matrix. Also, Telegram has a C++ desktop client.
Also, I would not advise to add proprietary repositories as you grant them root access to your system which is against security practices such as the principle of minimum privileges and defence-in-depth.
Same, it might conflicts a little with the desire to have a single application, but I want a native application for each platform which uses native UI and libraries. There's no reason a messaging app should be more than e.g. 40MB.
I would rather prefer browser app like Whatsapp/Telegram, I am not going to install extra app and switching windows to see chat when I spend most of the day in browser on desktop
