There is an existing Option that allows you to send New Player Tells to... Existing Chat Tab, New Chat Tab, New Chat Window. Would it be possible to create an Option to spend New NPC Tells to... those same three places?
Personally, I'd love to be able to have quest dialog show up in my main chat window along with the NPC emotes and the quest feedback chat, rather than have the first always open up a new window and the other two show up in my main chat window.