Surpassed the Teacher: Hatori Bisco herself is an example of this, given that she used to be tutored to an extent by Hino Matsuri, the author of Vampire Knight, who at the time was a more experienced mangaka (and Vampire Knight being more popular than Ouran to boot), whom Hatori greatly admired and looked up to. Eventually however, Vampire Knight suffered from Seasonal Rot and a steep loss of popularity along with it, while Ouran continued to climb the ladder of most successful shoujos, making it as far as to the top 10 list in Japan and even surpassing shounens such as Bleach (a rare accomplishment for a shoujo). In contrast, Hino Matsuri was told to end her story earlier than she wanted, her decrease in storytelling-quality and popularity not leaving Vampire Knight substainful enough for the LaLa magazine anymore (same one as Ouran was published in). Ouch.
What Could Have Been: Apparently, Hatori was originally considering Haruhi and Mori to fall for each other! This idea might be referenced in chapter/episode 7 where Haruhi blushes when Mori first calls her by name, and they spend some alone time where she's willingly carried around by him.
The bonus chapter about how Haruhi's parents met was originally going to be a full length chapter, but had to be shortened due to time limit.