I find that instead of trying to convince friends/family to use Signal I just tell them "use Signal as your default SMS app" or install it myself for them. This tactic worked well in the Internet Explorer/Firefox and then Chrome transitions, so I don't see why it can't work again.
Then whenever I will be chatting with them, it won't matter if they try to send me a SMS, as long as I use Signal, their messages will be encrypted, as they will be data messages. I wouldn't trust the default SMS app/Android Messages not to steal your SMS texts anyway, especially on Chinese phones.
Also, I can't wait until the Matrix-based Riot gets its redesign:
https://medium.com/@RiotChat/a-sneak-peek-at-a-whole-new-rio...