This is a good strategy for burning bridges that don't have to be burnt (and I mean between friends, not just random acquaintances who you don't care for). It's better to gradually shift person-by-person so that you don't lose relationships.
I have been through this 'transition' about 4 times now on other applications. "oh I do not use that one anymore I use XYZ" when it comes up and offer to help them setup a new account. I then usually just fire it up for them for a small conversation right then but then turn it off. There is nothing wrong with having more than one application. Hell most of our phones are already running dozens of them. But at a point you grow weary of them. I used to use aggregator applications like trillian. But they always seem to be chasing the breakage or not able to interpolate at all.
In a couple of years it will be some other application that will be the top dog. "Hey what is your ICQ number?"
It also depends if you are considered a hub or spoke in your social circles. If you are a 'spoke' then getting others to change would be hard. If you are a 'hub' you have better success.
If you lose contact with your immediate family because of a messaging platform it's not really a great relationship that needs to be maintained anyway. You can visit, call, text, or email too.
It's actually setting a healthy boundary. If they don't want to reach me on Signal, that's fine. There are other ways to talk to each other rather than text messaging.