However, I suspect that getting message-ids for all your pull requests
would significantly complicate your workflow.
Yeah, that would be a noticeable annoyance. If I were to process pull
requests the way I used to process emailed patches (ie "git am -s" on
a mailbox) that would be a natural thing to perhaps do, but it's not
at all how it ends up working. Having to save the pull request email
to then process it with some script would turn it into a chore.
I think the pr-tracker-bot clearly catches most cases as it is, and
it's only the occasional "somebody did something odd" that then misses
an automated response. Not a huge deal. For me it was actually more
the "I didn't understand why the response didn't happen", not so much
"I really want to always see responses".