Scan rendered node instead of body?

Problem/Motivation

Very few content types these days have a "body field". What if instead we scanned the rendered node, just like how SearchAPI can scan the rendered node for search indexing.

Proposed resolution

Rough idea:
1. Click a button on the node form that says "Scan current content"
2. Popup appears with summarized text
3. "copy" button next to summarixed text so that I can easily paste it into whatever field this node type uses for "teaser" or "summary"

Remaining tasks

1. Come up with a more detailed plan.
2. Build it.

User interface changes

API changes

Data model changes