Maybe the Giants would ask Kraft to talk to BB. That doesn't seem outrageous. I suspect Kraft would say ok too. Further, he is right that BB would initially own NYC. And if he brought Patriot type continued success to the Giants he would own it times two (NY media is hilarious in how they think being the toast of the NYC town is the end all be all).
That's about it on him being right. BB is 63 years old and has been headcoach-ing uninterrupted for 15 years. He has complete control of the non business side of the Patriots, an owner who who has complete and nearly blind faith in him, a football god to nearly all new england fans except media, probably compensated and will be compensated markedly-extremely well by the Patriots, and is on the cusp of taking the franchise to undeniably singular NFL success (it is very possible to see him in the next few years to have 8 Super Bowl appearances and 6 Super bowl wins over a single coaching tenure -- it would be undeniable in its singularity of 'legend').
So, umm, ya BB the 63 year old man is going to give that up to come in, semi-blow up a franchise and start the process over. In reality he will probably coach the Patriots a few years after Brady departs and call it a HOF career.