Jeff King [off-list ref] writes:
Right, I came to the same conclusion (we may even have discussed this on
the list, I don't remember). The current "todo" format says that only
the command and sha1 matter, and we'd be changing that. Maybe that's not
so bad if the user has to enable the feature themselves (and clearly it
would be incompatible with a custom format option).
If you are in the habit of always writing 4 or more lines, the
chance that you would make a typo on the line you can correct in the
"todo" list with such a feature is at most 25% ;-).
I think one downside is that a mere presence of such an option hints
that we somehow encourage people to commit with a title-only message.