Allow us to create quest trees in which one or two quests can go off of one quest that you've just completed. So as an example you could set up a world in which two factions exist and after completing the quest to discover both factions you gain two quests, each of which are joining either faction. You could also allow us to lock out some quests after completing another. Ex. If you join faction 1 then the quest for joining faction 2 says "failed" or "unavailable".