Between now and release I imagine organizing quests, and the quest system in general, will undergo many changes.  I think limiting players to one quest at a time would be pretty unpopular.  Furthermore, there will be a lot more sophisticated quests implemented, and I'd hate to be given a difficult quest which may take half the game to complete and not be able to undertake simpler ones in the meantime.

Well, strictly speaking the map shows the locations of the current quests, yes, but all the the quests you're on are current quests, so the map shows all of them. But I'm guessing that's not what you were intending to say. And you can get a list of open quests in the handily named "quests" screen in the kingdom info window (although the interface there needs some hefty improvements.

A suggestion I had was to use the Quest tab under the kingdom report to show you where you should take each noble you had. I had one game where I saved and came back later and had like 4 nobles and I kinda forgot where to take each of em (they were relatively close) and I had no way of double checking to know exactly what the objective was.

Maybe show a minimap when highlighting a quest under the Quest tab that shows the objectives as glowing markers, both the noble and his destination. Hope this helps or sparks some ideas