If Jackson is pissed at Kelly for whatever slight there is/was, signing with an NFC East team would be first on his list. Dallas doesn't have the cap room, and I am not sure how Jackson would mesh with Coughlin.
I always thought Jackson was overrated as a #1 receiver, but I will still take his explosiveness and playmaking ability on the Redskins. It would help the return game at times, and provide a great deep threat. A 1-2 punch of Garcon and Jackson is something that the Redskins have not had at receiver for years.