if not tied to background or for ex. what you were doing at the time you were abducted, would anyone be opposed to having class specific quests available for your pc? the original bg2 even had questlines where you could gain your own base by completing your class related questline or would that be too prescriptive?
Still too difficult. Ranger for example, just the favoured enemy part could indicate different past environment. Race plays another part, did you live in the Underdark or elsewhere. Natural explorer even, an urban tracker would not feel as comfortable in the forest as a beast tamer. To make a generalised quest for any of this I feel would have to be too shallow to incorporate anything worthwhile.
