A couple of things to consider most critically the cap implications. Remember on a lot of these big deals a lot of the money comes up front and the actual salaries are lower year to year. (see how Brady's deal worked). So if traded to us, all we would responsible for would be the yearly salaries and most of the guarantees would be gone. So on closer inspection it probably wouldn't be as big a cap hit as you might think.
2nd, on the surface it's a complete no brainer. You are giving up a player who really has no future on your team other than a back up, for a truly great versatile defensive player who excells at the most impactful position on Defense. A guy who makes everyone around him so much better.
3rd. His back injury is a concern, but even if I knew I would only get 2 productive seasons out of him, I'd make this deal in heart beat. Again, for what you give up, those 2 years would be worth it.
4th. It also makes sense to the Texans. They proved they can play good defense without Watt, and only need a competent QB to become an annual competitor. JG might be even better than that. They have proven they can be a playoff team even without a QB. This will give them what THEY need, and the Pats get what THEY need.
JG is going to be moved this off season. If they get a mid round first and a 4th, I'd be thrilled. If they got JJ Watt, I'd be extactic. There would be no words for my joy
Unfortunately its only a fantasy.