I'm not going to be able to help but merely add to the query. One idea I had was to use PhotoMechanic as a viewer for various social media sites - Flickr, Instagram, etc. PM is a great way to quickly review lots of photos. One would need API's from various sites - Flickr certainly has one - and then develop within PM the ability to use the API to import the photos and export the ratings on a site specific basis. For example, I could import 100 of my contacts photos, selectively 'fav' them (perhaps mapping PM's tag field), perhaps write a comment and then have the information added back to my Flickr stream.
I'd be interested in hearing yours or others thoughts on this.