RBF is not consensus - it's policy.

There has been nothing stopping nodes from accepting full RBF transactions, or from miners mining full RBF transactions, since day one of bitcoin. It is a local policy in Bitcoin Core to enforce opt-in RBF, but any node could have opted out of that and accepted full RBF transactions at any time, which is why zero confirmation transactions were never safe. The recent change to implement the full RBF setting simply makes it easier for nodes to do that, and will eventually move towards that being the default setting. But again, that will be policy, not consensus. Any node will still be free to reject full RBF transactions if they wish.