I've looked at RBF and my understanding was that it was totally opt-in? Older versions of Bitcoin core still work and can keep on mining. IMO that's less big of

I've looked at RBF and my understanding was that it was totally opt-in? Older versions of Bitcoin core still work and can keep on mining. IMO that's less big of a change because it's not breaking anything. I haven't actually looked at segregated witness though.