Currently, shared items via FB, google+, or Whatsapp use indiscriminate text extracts from the lead of an article. We have put a lot of effort into developing a 'card' summary for link preview, related pages and hover cards. We should provide that to social sites so that we are putting our best foot forward to potential users:
FB extracts its own, which often looks awful.
Here is an example from FB:
=Acceptance criteria =
 TextExtracts has a feature flag that when enabled adds a og:description meta tag to all pages in main namespace
 og:description is only added if a feature flag is enabled
 verify the description shows up in WhatsApp, Facebook and Twitter shares.