@fribbledom since quite some services already support looking for contacts by giving them access to your contacts list, I guess that could be a starting point.
The trouble is that I don't want to give anything full access to my contacts, so what we'd need is a way to indicate which fields you want to give them access to, and prefilter that list based on a key field with multi-value support (e.g. an audience/circles key with values such as 'work', 'family', 'offline contacts').
But based on the reaction of quite some people to Circles in G+ and Aspects in Diaspora*, I fear that the concept will be deemed too complex to gain mainstream traction.
I guess it's in part what #TimBernersLee is trying to solve with the #SOLID project (https://solidproject.org/).