We have already responded this in that thread:
While it may be interesting to raise the issue of the lack of key commitment in OpenPGP circles and it may be useful for some applications, in case of Delta Chat usage for messaging there is no need to do this attack because there is no transcript consistency in the first place - you can simply create two different messages with the same Message-ID and send different message to different group members. Providing transcript consistency would require more than adding key commitment.
AEAD (SEIPDv2) is already supported, enabling it in backwards-compatible way is on the “roadmap”: Generate Features subpacket on the new keys · Issue #6673 · chatmail/core · GitHub
As for key commitment without transcript consistency, even if it existed in OpenPGP, I don’t see the value of it. Original “Invisible Salamanders” paper is about the “abuse reporting” usecase where Alice discloses messages sent by Bob to Facebook.