I think it would just be cool in general to allow to user to specify if they wanted plain-text or HTML messages. Most email lists, CMS, and just about everything I run into still asks "Would you like plain text or HTML?"
I can appreciate it a little more now that I am a Smart Phone user, although admittedly, I used to think "why would anyone not want HTML".
I remember a similar debate back in the early 90's when ANSI art was popping up on BBSes. "My board does an ANSI detection before sending you the graphics", but some of my people connecting at 1200 baud just weren't having it!
