[edit] also a system of extended validation for signatures like for ssl certificates would be useful. I would end up expecting a nice green logo in my mail client for emails from citibank.com, something cit1bank.com could not achieve.
[edit2] also a modern design would require emails to be instantaneous. All these messenger apps would become redundant and we would revert to a common standard.
http://craphound.com/spamsolutions.txt
Good checklist of things a potential "reformed SMTP" needs to do.
If the Wright Brothers wanted to eliminate auto accidents by flying, anyone at the time could have told them they were doomed to failure, and history would have proven them right, even though air travel is safer than road travel. That's because getting people to stop using cars isn't simply a matter of inventing an airplane.
Someone should write up such a list along with a bot that replies to any post that cites the craphound link linked above. I think it's a valid counterpoint.
Nevertheless, whenever someone offers up a cure-all for SMTP, that craphound list is the first thing that comes to mind.