I see your point. Bob the e-mail user e-mails Alice the DC user a few weeks later, but they’ve set a subject that’s appropriate to what they’re talking about (because that’s how an e-mail user will normally behave), and everything is fine. Alice’s reply will be Re: Subject set by Bob.
However, I’m concerned in the other edge-case, when it’s the DC user initiating a new conversation with an existing contact. They’re done with their “Meet up at the park later?” conversation, and that’s the subject stored with the conversation. Two weeks later, Alice the DC user sends
You should see this hilarious video. It's a cat with a cheeseburger - that can't be healthy for it! http:// ....
and it’s received by Bob the e-mail user with a “Re: Meet up at the park later?” subject line. Alice the DC user looks like somebody who’s bad at e-mail etiquette. It’s not totally out of the bounds of normal behaviour, but it gets worse if they’re still doing it a year later.
Yeah, that could be awkward. I’m imagining that there’d be a simple heuristic when turning the body into a subject. Keep walking the text until you have more than N words/characters, and stop on punctuation. Alice writes
Hi Bob! Has Charlie talked to you about this weekend yet? We're going to take the train to ...
which turns into a subject
Hi Bob! Has Charlie talked to you about this weekend yet?
I’m aware that I risk overcomplicating the design, but I’m fearful about DC being seen as an impolite invader into the e-mail ecosystem. Personally, I only use it for group chats with my e-mail using friends, because it appears like ‘normal’ e-mail with subjects. I avoid using it for 1-to-1 chats. I don’t see this ever changing, as DC will always be in a minority compared to all of the regular e-mail users out there, but that’s the idea with DC - take advantage of an existing communications system with a huge network.