I don't really have a good idea how some kind of voting process would
look like where we get relevant feedback from a substantial number of
non-specialists.
FWIW, speaking as a Lilypond user with some programming experience (but who
is not a LP developer) -- I was skeptical of the change at first, but I'm
wholly convinced by David's point that \relative d'' { d e f } features a
redundant d that could be removed from the syntax by \relative { d'' e f }.
The fact that it's a new rule doesn't make it a bad rule. I think I would
adapt to this syntax easily.