If I understand right, from a SolrDocument, you need to get the _values_ of each schema.org attribute, including the proper value for the itemtype. 

The doc extension framework stuff is a way to have those looked up from the document, in ways specific to the type of document, even for hetereogenous results. 

Maybe I'm not understanding what we're talking about. Otherwise I guess what I'm trying to explain is not engineered in a way that is usable by other developers, since I can't figure out any other way to explain it. Oh well, thanks for listening I guess.