That deal is very interesting. Lee's year was much better than it looked, as he had little run support (6-9 record, with a 3.16 ERA). Still, I'd be a little wary at 34 coming back to the AL. However, I believe he only has 2 years left, so it fits in with the Sox's payroll plans.
Unfortunately, I don't think the market for Ellsbury is going to be large. It's a good idea to trade him, but given his health woes that lead to his subpar season and the fact that he becomes a FA next season, I don't see many teams giving up more than a mid-rotation pitcher for him.
And there's no point in doing that. We have enough of those already.
So we might as well hold onto him. He has more value helping us make a run this year or being dealt at the deadline after he establishes his health.