I'm the author of the proposed patch. I'll be blunt: it's a bit late to revive this offer. I'll try to work on it next week, with no guarantee I'll succeed in a limited time. Comments on the technical documentation I submitted in 2012-07 would be much appreciated.
Now, I'll try to be constructive, but I'm on for a big rant.
On the technical side, the patch was developed for Moodle 2.3. We proposed it more than 13 months ago. Unfortunately, there were changes in the "user profile" API in v2.4. IIRC, these changes were undocumented in the wiki, and unused in the PHP code of M2.4, yet they were added to Moodle. We chose not to port them when we migrated our forked Moodle to v2.4. I mean we have a working patch for Moodle 2.4 (in the same github repository), but the new (unused) 2.4 profile API was deleted because it would have duplicated our own API. I haven't looked at v2.5, but if this new API is used, it will conflict with ours. Even setting this aside, there have been 13 months of Moodle development, so it would be a hard work to replay this massive patch on the master branch.
On the human side, I haven't worked on this part of the code for months, and I'm reluctant to go back to it. Seeing how the previous internal process of "investigating the more general solution" went immediately astray then died with no visible progress (see forum link in a 2012-11-19 note above), I'm not confident that Moodle's team has an idea of what they think suitable for generic metadata. The new profile API I've talked about is another reason for my disillusion: if generic metadata were being investigated, then introducing an API for user-specific metadata was a bad idea, and probably shows a lack of internal communication. I'm afraid I'll redo this patch for nothing. One year ago, did anyone at least read the technical documentation I submitted with the patch?