I think you are pretty close to getting it right. This spec is Dead on Arrival. This spec will never get traction in a large corporate environment. Primarily be

I think you are pretty close to getting it right. This spec is Dead on Arrival. This spec will never get traction in a large corporate environment. Primarily because the business has a need to monitor and archive employee emails. As a result no large corporation will ever adopt end to end encrypted email as a standard. While in the consumer arena Gmail and other ad / user profile supported business' will never adopt this as it limits their access to valuable user data.