There was a discussion about improving fee estimation in Bitcoin Core last year in which 'instagibbs' mentioned that we cannot consider mempool as an orderbook in which which everyone is bidding for block space because nodes can use different relay policies: https://bitcoin-irc.chaincode.com/bitcoin-core-dev/2021-09-22#706294;

Although I still don't consider fee rates used in last few blocks relevant for fee estimation, it is possible that we have nodes with different relay policies.

Similarly if we have different RBF policies being used by nodes in future, how would this affect the security of lightning network implementations and other layer 2 projects?

Based on the things shared by 'aj' in

https://lists.linuxfoundation.org/pipermail/bitcoin-dev/2022-February/019846.html it is possible for an attacker to use a different RBF policy with some nodes, 10% hash power and affect the security of different projects that rely on default RBF policy in latest Bitcoin Core.

There was even a CVE in which RBF policy not being documented according to the implementation could affect the security of LN:

2.With recent discussion to change things in default RBF policy used by Core, will we have multiple versions using different policies? Are users and especially miners incentivized to use different versions and policies? Do they have freedom to use different RBF policy?

3.Are the recent improvements suggested for RBF policy only focused on Lightning Network and its security which will anyway remain same or become worse with multiple RBF policies?