I love Hayward's game. For that matter, I love Jimmy Butler and Paul George's games, too. Hayward is 27 years old. Does his game have another gear once he gets under the tutelage of Brad Stevens? Or is he at his peak?
Personally, I wouldn't do it. I'd focus on building around our young players, because Hayward+IT+Horford as our core simply isn't good enough, at least not until if/when our youngsters mature, and if we make that move, we're hamstrung on doing much of anything else.
IMO, the centerpiece of the franchise from now going forward should be Brown and Fultz, plus hopefully another great prospect from BRK 18.
What if the young players don't turn out like we hope, you might ask? Well, we won't win a championship with them as our core. But then, we aren't winning one with Gordon Hayward either if Jaylen Brown and Fultz bust. Adding Hayward solidifies our spot as #2 in the East, but IMO, it doesn't move anything enough to get us past CLE or GSW. I think those teams are just too far ahead of us until they get broken up for Lebron gets old.