On Sun, Apr 06 2014, Jani Nikula <jani@nikula.org> wrote:
> Add a tool to start composing an email in the Notmuch Emacs UI with
> the specified subject, recipients, and message body.

Hey, Jani.  You might be interested in checking out a patch I submitted
a while back to support "mailto:" urls in notmuch-mua.el:

id:1327865624-7673-1-git-send-email-jrollins@finestructure.net

That, combined with your new ui interface would make handling mailto:
urls in say browsers very convenient, e.g.:

  ELISP="(notmuch-mua-mailto \"$URL\")"

for:

  notmuch-emacs-mua mailto:foo@example.com

jamie.