The following doc proposes a mechanism for introducing share referral identifiers in AMP.

One relatively recent, and apparently very effective, development in “social media optimization” of content is to utilize fragment URLs to attach shared URLs to a particular page view. This allows tracking of viral shares and the resulting page impressions back to the original share across multiple social networks, instant messaging applications, etc.

Supporting this in AMP requires:

• Expose new amp-analytics vars for “incoming share tracking identifier” and “outgoing share tracking identifier”.
• Implement URL updating, including update of URL in viewer (e.g. search results page).
• [Not in v1, but possibly future version] Expose a method by which a publisher can specify the “outgoing share tracking identifier” that should be used and set in the URL fragment after the page has loaded and the incoming share tracking identifier, if any, has been recorded.

For details see https://docs.google.com/document/d/1TSUhvA7O1fDiiI3ZznmHU4SY8iAC0kT6W0-ezMDyweQ/edit?usp=sharing

/cc @cramforce