Creates a fine mess on the network, defeating essentially the purpose of non-RBF; especially due to the former.
This will indeed be the beginning of the end for non-RBF transactions, as I suspect before long most miners will choose to look at mempools which are opted in to full RBF to allow them to maximize their profits from fees. I guess zero confirmations transactions will be a thing of the past unless the two parties involved completely trust each other.
Here are the final commits to be merged in to the main branch:
https://github.com/bitcoin/bitcoin/pull/25353/commitsIf all goes to plan then this will be live in the next version of Core, 24.0.