My only concern with bringing Harper up to start the season is where do you bat him? They probably want to bat him low in the order which means we still need LaRoche to break up the RH 3-4-5 of Zimm/Morse/Werth.
Would Davey be comfortable with Zimm-3, Morse-4, Harper-5, Werth-6?
If they don't sign a lead-off / CF type, then you could play Morse and Harper in the OF at the same time and still have LaRoche at 1B, but then we still don't have a lead-off hitter (unless Reyes replaces Desmond).