I would be happy if there was a subset of HTML for email. Look at the HTML Gmail produces, which is essentially just <div> or <p> in the default mode and uses <span> for changes of formating and <blockquote> for replies. This would work for propably 90 to 99% of all hand written emails in Outlook or any other email client.
I understand the procrastination argument but if it is not some (social) website it is something else. People who tend to procrastinate will do it anyway.