I also think it'll hurt the value proposition when getting people to join signal. Not overcomplicating the messaging scenario was a big winner to do that.
A user already has:
- Telegram
- Facebook Messanger
- Instagram that has direct messages
- the good old email, or better, many of them
- Microsoft Teams for company communications
- Discord for communications with group of friends
- the old SMS (that I didn't even know that in some parts of the world were still used, since I receive them only for 2 factor codes, notifications about my card transactions, and spam)
Adding another app is that a big deal? By the way I don't use Signal, but not for the reason of not having another app on the phone, just because I don't know anyone that has it and actively use it.
That's why it was a huge advantage that, on Android, Signal could replace a SMS client. You weren't adding _yet another_ messenger to the list, you were replacing the SMS client with one that could send secure messages. That made "switching" to Signal (which, ofc, was not a switch at all for my friends who use SMS) much easier for me. I could continue texting my friends and seamlessly switch to secure messaging if they ever got signal.
Contrast this with my friends who kept their old SMS client who reliably forget to check / use signal and generally tend to go back to texting me in a few weeks. Even if you send 0 signal messages for a long time, by switching you SMS client you are already setup to receive them and will habitually open an app that supports E2E encryption.
For example - Facebook Messenger also supports sending and receiving SMS messages - likely because they've done the research and found it drives adoption.
Hell, even my aunt that doesn't know nothing about technology has WhatsApp and had me install Telegram because the church opened a channel on it!
Also use DMs on Twitter relatively frequently.
Personally, I use only two of those apps you listed for messaging, and for all the others, I say, "Sorry, I don't use that one."