they need to make the recolors and variants of store/etc mounts, quest chain obtainable from the expac they were released in originally. example:
quest chain for vanilla golden palamino in azeroth
quest chains for collectible card mounts and special event mounts just as recolors.
quest chain for seasonal mounts - recolored.
quest chains for discontinued mount recolors.
same for battlepets. recolor/re-release as quest rewards