Emissary Quest Chain

I think it would be interesting to have quests to be an Ambassador to cities, your own faction cities, and the cities of the opposing faction. Do do it in opposing faction cities, you could get an Ambassador's banner, so the guards won't attack you, and so that you won't be PvP flagged on PvE servers.

You could do many things, from message delivery, to gaining the ability to do certain opposing faction quests, so that you could pick up Horde quests if you're Alliance, and vice versa.

For an example, an Alliance character might have to deliver a message to Thrall in Org, and when they do that, Garrosh Hellscream could could and make them prove themselves in the Ring of Valor, having both strength and honor. After that, high level Horde quest givers in certain places would now offer quests to that Alliance character. It's just a thought.

The quest chain could be long and hard, and the player could have to learn language skills, which would only work during quests. And they could do diplomatic missions to Neutral factions and races. Or even try a couple to hostile mob places, and turn them neutral. To do Diplomatic missions to the Horde, as an alliance character, they might have to start by going to small villages, and earning letters and other things which would eventually allow access to city missions, on quests.