I love the idea, and I'm looking forward to ticking the "block all incoming enriched calls" box.
I currently use a (3G) feature phone for my calls and SMS that I bought from Amazon. That does get a few spam messages but I know to ignore them and block the number. I have a smartphone which I use for WhatsApp - because the rest of the family do - and email/the Internet. Anybody who calls or sends an SMS to that phone will find that it isn't read/answered. The same will apply to any RCS messages if I can't disable/delete the app or block it.