Well he did say he'd behave "most of the time." I'm sure he's still got some shenanigans planned for the future, just minor pranky ones. XP XD Now that'd be an Episode, Discord and Pinkie doing pranks! X-0 Pinkie could teach Discord that sometimes you can go too far w/ stuff like that.
Welcome ^^ Yup, I guess I wanted that too, but to me the most epic way to see a villain becoming "good" is when he has to ally with the good guys, finding out they're kinda cool after all... It would have been awesome to see them fight together and Discord letting out a "Heh, you're not bad, ponies" in the end ^^ Ok, headcanon stops here. Sorry XD