I also thought about it, but didn't want to propose it myself. But I
agree that this would be a reasonable change. After all, git-repo(1) is
still young and it's marked as experimental, so from my perspective it
is fair to do adjustments like this once we notice that we've been a bit
too narrow-minded.

So I'm all for it.

Agreed. And I think that it makes more sense than adding a new output
format only for --keys and extra checks in other places.

Besides this, I sent first patch of this series (the "default" output
format) to support -z with --keys [1]. If we change "keyvalue" to
"lines" maybe it wouldn't be useful.

So, now I'm thinking about dropping the first patch and replacing it 
by a new one renaming "keyvalue" to "lines".


[1] https://lore.kernel.org/git/5A4D4433-FD38-4BB0-81B6-3BAD33A30A74@gmail.com/ (local)