When ToT was released, I felt it should be an added app as well. Just let us log into our account on mobile/tablet, select a character, let us play ToT(NPC or PvP), and mail the win/loss rewards to that selected character. Which we have to open in-game when we log into the game again.

But that is honestly the only thing in ESO which should be an app. As in-game mail is only received when a character logs in, so an app for that won't really work. Maybe an e-mail when something is sold, could work. But that wouldn't require an app.