To be fair I do not think we have had enouth time to fully discuss and understand this issue, I was only made aware of it being implemented relativly recently.

Recent RBF discussions going back to May 2015.

Github: https://github.com/bitcoin/bitcoin/pull/6176 - Add first-seen-safe replace-by-fee logic to the mempool #6176 https://github.com/bitcoin/bitcoin/pull/6352 - Scheduled full-RBF deployment #6352 https://github.com/bitcoin/bitcoin/pull/6871 - nSequence-based Full-RBF opt-in #6871

IRC meeting: https://www.reddit.com/r/Bitcoin/comments/3t1in5/bitcoin_dev_irc_meeting_in_laymans_terms_20151112/

There are many other logs which can be found at http://bitcoinstats.com/ for #bitcoin-dev and https://botbot.me/freenode/bitcoin-core-dev/ for #bitcoin-core-dev

Mailing list discussions in no particular order:

https://lists.linuxfoundation.org/pipermail/bitcoin-dev/2015-November/011783.html - [bitcoin-dev] Opt-in Full Replace-By-Fee (Full-RBF)
http://lists.linuxfoundation.org/pipermail/bitcoin-dev/2015-May/008248.html - [Bitcoin-development] First-Seen-Safe Replace-by-Fee
http://lists.linuxfoundation.org/pipermail/bitcoin-dev/2015-May/008232.html - [Bitcoin-development] Cost savings by using replace-by-fee, 30-90%
http://lists.linuxfoundation.org/pipermail/bitcoin-dev/2015-July/009420.html - [bitcoin-dev] Significant losses by double-spending unconfirmed transactions
http://lists.linuxfoundation.org/pipermail/bitcoin-dev/2015-June/009253.html - [bitcoin-dev] BIP: Full Replace-by-Fee deployment schedule
http://lists.linuxfoundation.org/pipermail/bitcoin-dev/2015-February/007404.html - [Bitcoin-development] replace-by-fee v0.10.0rc4
https://lists.linuxfoundation.org/pipermail/bitcoin-dev/2015-November/011685.html - [bitcoin-dev] How wallets can handle real transaction fees

Satoshi originally introduced unconfirmed transaction replacement https://github.com/trottier/original-bitcoin/blob/master/src/main.cpp#L434 but this was disabled due to a DOS attack (which Peter fixed by requiring a higher fee for each replacement).