Most teams have a young up and comer of their own in their system or already entrenched at 1B and if the Reds could get Ellsbury for Alonso, they should do it right away IMO.
No chance of their being able to peddle Alonso for Ellsbury. Sox have Lars Anderson and Anthony Rizzo as 1B prospects -- and Alonso has not separated himself with any certainty from guys like that as of yet. Red Sox have bigger fish to fry.
It makes sense for the Reds to continue to develop Alonso at AAA. Hopefully he puts up big numbers in 2011 and makes himself a real option for teams looking for a young 1b/DH who can step right into a major league lineup. He's not quite there yet.