You could probably mod them back in. There are still quests that allow you to recruit champions, so the mechanism must still be in the game. I don't miss them in the least, though the world does seem a bit empty without them.
The solution in my mind would be to make the Quest markers have visible units from the map. So quests would look like FE's champion recruitment things, but instead of the champion, you'd have the quest-giver.
