Retire MPD

[N. W. Perry]

In light of this thread:
https://forums.ldraw.org/thread-24589-po...l#pid41128

I'd like to renew my call to retire the MPD extension and to go LDR only for model files. All software that claims to be LDraw compliant should implement the MPD spec and there is functionally not difference between the two. Since it clear that at least some users are confused, I'd like to simplify things.

If my understanding is complete, the reason to keep .mpd is that it tells the user at a glance something about the content of the file—i.e., that it contains submodels, or more specifically, subfiles, as reflected by the format's only metas (0 FILE and 0 NOFILE).

Is there a way to readily convey this information to the user other than by way of the .mpd extension?

Are there any other affirmative reasons to keep .mpd? (By that I mean reasons that specifically require keeping it, as opposed to reasons not to retire it.)