https://wicg.github.io/cross-origin-embedder-policy/ is an explainer / monkey-patch spec that attempts to crystalize the discussion in whatwg/html#4175 into something we can get to work implementing, writing tests for, and shipping.

Please file issues with this document against the whatwg/html repository to keep the conversation in one place: https://github.com/whatwg/html/issues/new