If he has a good season Boras will price him out of Boston as weird as that sounds.
Ellsbury has value right now but it's hurt by his injury history. It's best to hold onto him and hope he stays healthy and produces to increase his trade value. It's good for all scenarios. Jacoby good, Red Sox stink, they trade him to a contender. A Beltran type return is very possible. If Jacoby is good and the Red Sox are good, they keep him, offer him a QO and collect the pick from Seattle after they give him 100M+ lol. If they both stink they can trade him for whatever as they probably won't be offering a QO anyways. And Bradley comes up to replace him, giving us all something to look forward to next season.
The other scenario is trade him now for probably lackluster return, rush Bradley from AA to ML and hope it doesn't screw him up.