Why does Zilean have to be a "cool mage" or "badass"? Aren't there other traits that could be considered appropriate for the old time wizard, or traits that would make him attractive in a way that only Zilean could be?
While I don't like to talk too much on the Trundle changes, it's similar to how you guys said "alright, we know this guy has niche appeal because he's scrappy, sarcastic, and runty, but wouldn't he be more cool, wouldn't he be really 'badass', if we beefed him up a bunch, made him king, and had him shout a bunch of hammy one-liners?" Now, that isn't to say that this sort of character doesn't have any appeal, but you end up with something of a "personality net-negative" when you throw him in with other "dumb brute" archetypes like Mundo!
Part of having such a large and diverse roster of champions, is that you have one of the biggest opportunities to really allow for niche appeal in a lot of them. You have room to really look at any champion out of the 110+ you have right now and really think, "Alright, how can we make this character appealing in a way that only this character could truly hit all the right notes on?" This is something I've felt you (collectively) have really hit home on with champions like Braum, Jinx, Vel'Koz--hell, a lot of the new champions, to be honest--but not so much on reworks like Trundle or Nasus, where the solution seemed to be "make them bigger, meaner, and crank up the 'badass' to 11." Keep in mind that you're an ice cream parlor with over a hundred flavors, so never be afraid to do a bit of exploration and stay true to a flavor that might not be the most popular or least polarizing! Cotton candy, for example, might not be the most popular flavor, but keeping it in stock won't chase away the masses of vanilla fans and chocolate lovers!
I don't think I'll speak on this much more in the future, but it would be great if you (collectively) would keep in mind that there's hundreds upon hundreds of ways to make a character appealing, and that the question instead should be, "What kind of appeal could this champion and this champion alone really hit out of the park?" I might not be the target audience for Keeper of the Light-like doddering old dudes, but that doesn't mean that there isn't an audience for them!