1. This solution eliminates the decentralized nature of email.
2. No solution for corporate customers who would want to keep their emails private.
3. How would new contacts form?
Probably? You think there is even the slightest chance that fortune 500 companies would consider this? I noticed in your profile that you are a patent lawyer. What do you think would happen if you brought this suggestion up at the next partners meeting?
Respectfully, I think you are mistakeningly assuming that your email use case is representative of the rest of the worlds. Are you subscribed to any mailing lists? Do you ever engage in long form conversations with people in another timezone? Any non-corporate collaborative work with friends (software/volunteer activities/fiction/nonfiction writing)?