I think there is a better way out to solve this:
Just as in forwarding, there could be two ways to quoting text in a
reply - either reply inline or put the quoted text as an attachment.
Now the reply inline feature is meant for people who would like to
interleave their matter with the original, in order to maintain a sane
flow of thought.
For the kind of stuff that Peter (the OP) wants, we could have a
second way - attaching quoted text. That way, what the reader sees is
only the reply, along with the signature and all. And if the reader is
interested in the earlier messages, they are always available as
attachments.
Since mozilla already has the option to send forwarded text as an
attachment, why can't something like that be done for replying as
well?
I had posted this suggestion earlier on npm.wishlist where the
discussion started, but I had assumed that this feature already
exists. Now I know it works only for forwards and not for replies.
Ashant.