This would unnecessarily and extremely negatively impact merchants and users who choose to accept 0-conf while using mitigation tools like GAP600. This negative impact could be avoided by simply adding first seen safe rule - ie a trx can be replaced but needs to include the original outputs.

At GAP600 we continue to see strong use of our service for BTC we have seen circa 350k unique trx hash per month (over the last 3 months) requested to our platform. Our clients include - Coinpayments, Coinspaid and Changelly. Given the period of Mempool being full we have seen an increase in the fee required in order to be approved by our platform for trx. This is not an insignificant use case and one which can be easily maintained as is.

We have provided further statistics in the past and direct feedback from Coinspaid CEO with in the mailing list see here - https://lists.linuxfoundation.org/pipermail/bitcoin-dev/2022-December/021240.html

We have not seen any impact of full RBF on double spend rates for our trxs which seems to put in large question the stated figure of 40% adoption by miners at such a rate of adoption we would expect to see a large increase in double spends. We expect once this setting becomes default this will greatly change the adoption of this service.