I'll also add that I wouldn't even call what he's showing "semantic web", even in this limited form. I would bet that most of the people who add that metadata to their pages view it instead as "implenting the nice sharing link API". The fact that Facebook, Twitter and others decided to converge on JSON-LD with a schema.org schema as the API is mostly an accident of history, rather than someone mining the Knowledge Graph for useful info.
I'll also add that I wouldn't even call what he's showing "semantic web", even in this limited form. I would bet that most of the people who add that metadata to their pages view it instead as "implenting the nice sharing link API". The fact that Facebook, Twitter and others decided to converge on JSON-LD with a schema.org schema as the API is mostly an accident of history, rather than someone mining the Knowledge Graph for useful info.