Something I'd really like to see if a protocol that is designed for notifications to humans. Anywhere from "Your car is ready to be picked up" to "We charged your credit card for this product, for this month of server", etc, etc.
I think if it is built from the ground up as a notification protocol, we can avoid the crap emails that we filter based on regular expressions, and bulk mail, and recorded phone calls.
But, it'd be really hard to get any sort of traction on of course.