My first idea is not a new quest type exactly it is more of a variation of a current quest. I have seen a few times NPC's ask you to help them beat someone but you kinda do it yourself (Or they don't help). Why not have some of them NPCs join your battle when you enter the arena they could act like henchmen while in the duel and will cast spells for their respective schools and proper levels. this will help wizards who have difficulty with certain quests. you could also make this option optional in your options menu!
My second idea is a new quest type (there is a few quests that ask you to do something similar) you could have "Escort" quests a NPC asks you to help them find someone, something, or just simply give them a tour! you could have it so your pet (if you have one) vanishes temparaily and the NPC takes there place and walks next to or behind you while you lead them to their destination(s).
The first idea isn't bad, but Henchmen aren't exactly helpful all the time. Maybe if you've failed to complete the quest a couple of times the quest giver could say something like "Maybe you need some help" and can show up when you start the fight. The only problem I see here is that it would defeat the purpose of Henchmen, which you have to buy with Crowns.
The second idea is something for the lower levels. I could see a "tour"-style quest working in Wizard City, but not in Celestia. Not sure about KI working it into the next world, but I'm sure if KI wanted to add quests to the lower worlds they'd use these ideas.