On the tahoe-dev mailing list, Zooko suggests:

I really like using the mailing list for patches, because the mailing list is a public, on-the-record conversation that includes everyone.

What about this:

  darcs send -o patch.darcspatch
  darcs diff -u -p"${PATCHRE}" > patch.diff.txt

and then send both to the mailing list as attachments? This is more work for the submitter, as they have to attach the files to a message and send the message (instead of allowing "darcs send" to send the message for them).

The good things about this are:

• hopefully everyone can see the patch contents in-line in the mail, and
• you can add a "cover letter" -- a message to the mailing list about the patch.