For clarity, Quim’s examples (of GitHub resources, specifically) are all hard-coded by OneBox and not achievable by Phabricator (or other third-party software) using OpenGraph tags, right?
For example, the “Opened by (author) on (date)”, “changed x files with…”, “Enhancement” tag, and the text formatting in his examples are because OneBox hard codes various GitHub layouts:
…and it doesn’t appear that a similar rendering is possible through OpenGraph.
We could conceivably achieve something similar by submitting a pull request to OneBox, but such a request wouldn’t necessarily need to use OpenGraph (it looks like the GitHub layouts use an Accept header to retrieve the resource in JSON, and ignore the OpenGraph metadata on the pages).
Also, I couldn’t find it documented anywhere, but Discourse appears to require an og:description property in order to OneBox a URL (ultimately in whitelisted_generic_onebox.rb::has_text?). This isn’t required by the OpenGraph spec linked above (og:description is “Optional Metadata”), which led to some confusion.