I wouldn't rule out Hayward leaving Utah. He already said he will go where he feels he can win a ring, and Utah has struggled a little bit as of late.
Boston has been on fire lately, and Hayward fits our needs. The Butler/Stevens connection is a huge plus as well.
Boston recently beat Utah. We are already better than they are, and adding Hayward would make us even better than we are now. I'm sure he has at least thought about playing in Boston.
Edit:. Just wanted to add that Hayward in Boston would mean a shared load for both Gordon and IT. Each of those two are being asked to play the lead role offensively for their teams, and would compliment each other well on the same team.