You misunderstand the point being made. The argument is that most home users push their mail over JSON over HTTP (or something) to an intermediary like Gmail that does trust them (because it authenticates them), and the intermediary sends the email over SMTP.
There is no proposal to make SMTP use HTTP as a transport. The point being made is that, despite most people having email work fine, most people do not directly use SMTP on their home computer, and instead use HTTP to access access some other machine that _does_ use SMTP. So it is not contradictory that port 25 on the home user's side of the connection does not work for most people, even though most people do use email.