Yes, a conversation editor is sorely needed.
Some have already noted that for various reasons, chief among them
that someone changed the subject header, Gmail often fails to
recognize that an incoming message is not put into the conversation it
belongs to but into a new conversation. It would be nice to merge it
in where it belongs.
Besides that, sometimes people change the subject without touching the
header, as when seeing a message from you somebody who wants to
contact you about something else just replies instead of composing a
new message. When moving a message from one coversation into a new
one, it would be nice to change the subject header. The G Groups (and
if I recall correctly, Usenet too) convention of adding "Was <old
subject> to the end of the new subject header would be fine.
Taking it a step further, a tree view, like the one G Groups offers,
would be nice. I understand that it would muck up the interface, which
is pretty slick on the whole, so I can live with the flat,
chronologically ordered list.
[I would have preferred to reply to the original post, but's it's old
enough that G Groups doesn't allow replies. Replying here was the best
I could do for getting close to the root of the tree.]
</Fred>