Hello so when you reach max lvl the game begins to begin getting a lil bit boring cause you gotta wait a week to get into raids again so most people begin to collect mounts and theres not a lot, my suggestion is to add a lot more and make the mount system like in bfa so you can search the mounts and stuff and add more vendors across all of the map that sell nice looking things for transmogs or smthing, the realms on warmane are rly popular and i think if u add a lot more content to the game you would profit a lot thanks and please read this.
There are like hundred of different things to do. There are a lot of mounts to obtain by reputation, achievments, high end raiding, farming 70 lvl dungs/raids, doing north dungeons, pvp honor rewards etc etc. I highly doubt we need any custom NPCs or mounts in wotlk.