The Avatar team’s approach is posted at Common Core Ontology with Linked Data.
We’re renaming our Common User Profile to call it ‘card+,’ since it allows compatible card extensions that all conform to the Common Core Ontologies (CCO).
Since this group seems to have consensus on using FOAF for the Solid Card, we will post a solution soon that is both FOAF and CCO compatible, plus allows compatible extensions.
More will be posted within a week or maybe two.
Jim Schoening