Similar to how Acoustids are currently handled, it would be nice to have an external database linking to musicbrainz that adds support for storing Pleasurize Music Foundation-compatible dynamic range values.
http://dr14tmeter.scienceontheweb.net/index.php?title=Main_Page is a free, open-source command line tool for calculating dr14 values. It could be hooked up with a picard plugin to allow submission and tagging. THis picard plugin could also make them available as internal tags (_release_dr14, _track_dr14)
The tool needs to be modified to allow passing in a list of filenames on the commandline [ github issue added –Hawke], and make sure it can output to stdout in text format. [It does, via the -p switch but see this github issue as well. —Hawke
Site must have an API to allow lookups by release mbid. Submissions would be by api key, probably with musicbrainz authentication (like acoustid). How to handle multiple varying submissions for one release? I like medians. [Median could result in a decimal DR value, though this is unlikely. —Hawke] Filtering out bad submissions might be an issue.
A userscript could be written to allow displaying DR numbers on the release group, release, recording pages. (This is the main draw, really.)
There's possibly enough info on the official DB to allow semi-automatically importing DR submissions from there (catno, barcode): http://www.dr.loudness-war.info/