Matrix bridges solve a lot of this problem, though... aren't really reducing complexity at all ends of the system. It does radically reduce end user app complexity, though.
I've been hosting a Matrix homeserver for... oh, 4-5 years, now, and I have bridges installed for my use and a few other people who use it that bridge Signal, Google Chat, Facebook Messenger, and maybe one or two other services into Matrix - so I almost never have to bother with the other clients, I just use a Matrix client everywhere. There are the occasional quirks you have to deal with, most of which are solved by upgrading your bridge (and the new bridges are a lot easier to deal with than the older ones).
As people decide to go Matrix-native, I can talk to them that way as well.
That said, as far as non-Matrix options go, Signal seems to be a fairly common one and easy enough to get people to switch to.
https://docs.mau.fi/bridges/go/setup.html?bridge=signal is the setup for the Signal bridge, and you'll also need to look at the initial config setup. Once you have a working Matrix homeserver, it's mostly "Create a new database table, point the bridge at it, add the proper incantations to your homeserver config so it knows the bridge is permitted, and start things up."
I don't find it bad in the slightest, but I'm also a legacy Linux sysadmin sort.
If you're a GUI-only sort, it will be painful. If you're competent with older styles of Linux sysadmin, it's fairly straightforward, though getting Matrix federation working reliably can be a slight pain. Just make sure your certs update...
Alright that doesn’t look too bad at all. I’m not at the level of sysadmin, but I do daily drive Debian and generally know my way around a terminal. I’ll give it a shot!
I've been hosting a Matrix homeserver for... oh, 4-5 years, now, and I have bridges installed for my use and a few other people who use it that bridge Signal, Google Chat, Facebook Messenger, and maybe one or two other services into Matrix - so I almost never have to bother with the other clients, I just use a Matrix client everywhere. There are the occasional quirks you have to deal with, most of which are solved by upgrading your bridge (and the new bridges are a lot easier to deal with than the older ones).
As people decide to go Matrix-native, I can talk to them that way as well.
That said, as far as non-Matrix options go, Signal seems to be a fairly common one and easy enough to get people to switch to.