I'm writing an email at work when I realize, wait, this is one of those long emails that nobody reads. And I know why. It's the tacking on of the nice-to-haves--the stuff I just know someone will ask--that does it, that tips it over the edge, off into scary-looking essay land.
That's why we need an easy way to add accordions and popovers into emails, both of which were designed to reduce information overload. Email is already the de facto company wiki, why not empower it just a little bit more?