↳ In-reply-to » I’m still more in favor of (replyto:…). It’s easier to implement and the whole edits-breaking-threads thing resolves itself in a “natural” way without the need to add stuff to the protocol.

I just realized the other big property you lose is:

What if someone completely changes the content of the root of the thread?

Does the Subject reference the feed and timestamp only or the intent too?