I've been thinking this would be a fun topic to discuss. You have to consider the Red Sox will be looking at free agents as well. In order to be a player in the Red Sox outfield you really need to show something and be a top player. My thoughts on those player:
Luis Soto, Brandon Moss, and David Murphy don't quite have what you are looking for on the Red Sox roster. Out of the three I like David Murphy and he is a nice guy to bring in should the Red Sox run into injuries. Down the road I don't see him sticking around.
Jason Place is a guy you just sit back and watch him develop. There is no way to tell at this point if he will be anything good. I would expect him to spend a couple years in A-ball then AA-Portland at 21 years old and AAA-Pawtucket at 22. Chances are things don't go that smoothly.
Jacoby Ellsbury is going to be the real deal (barring injuries) and I would expect him to be the Red Sox CF of the future. When the Red Sox decide for that to occur you can expect Coco Crisp to move to either LF/RF or be traded.
My overall thoughts: Theo Epstein and the Red Sox organization seem to be leaning toward players who are complete ball players. Kevin Youkilis, Trot Nixon, Mike Lowell, etc.....complete players who are top defensive players and good solid hitters. If Willy Mo Pena can turn into that type of player who is solid in the outfield and patient at the plate then he will stick around.
Its almost impossible for us to predict what the Red Sox outfield will look like in 2010 but if I was to guess: CF-Jacoby Ellsbury, LF- Willy Mo Pena, RF-Matt Holliday