Its really hard to say where Upton will play. Carlos Gonzalez is progressing a lot faster and will more than likely get the call before Upton. Carlos undoubtedly has a great future, so I think its safe to say that if he hopefully does not get traded that he will have a starting spot intact. Upton would then be left out with, as you mentioned, Quentin and Young already showcasing the talents that caused them to be so highly touted. Ultimately I think the position that Upton will wind up at is 2nd base, due to the fact that the Dbacks don't really have another decent prospect or young established starter at that position. Another possibility is for Tracy to be dealt, but that would only happen if his struggles this season continued into the following seasons. I highly doubt this will be the case and Tracy will once again establish himself as one of the cornerstones to their offense.
On a side note, where have you been that you didnt hear one of the top 5 prospects in baseball had his position changed? I know its a rather small detail to be aware of, but you seem to be fairly knowledgeable about the top prospects in their organization. Not to mention the fact that stories about Upton are top discussion topics at many sites aside from this one. Its all good, but it is rather puzzling.