The big key to all of this, is that Boston has a back deal handshake for Carmello/LeBron. Without that, they don't do anything. I think Carmello is more likely. Also, Utah would have to decide that they value Embiid/Randle/whoever is available at Boston's pick more than overpaying Hayward. Kanter, in my opinion, is another Al or Boozer. I like him, but if I can move him for something better, I do it.
So, if Boston knows they have Carmello and Rondo, they need pieces around those two. Ainge likes to build with known quantities and not unknown (he is probably the smartest GM out there. He sent Big Al, Ratliff, Telfair, and Gomes to Minn for Garnett. He also sent Sczerbiak, Green and West to Seattle for Allen). This speeds up the rebuild and you know what you are getting. The potential for "busts" drops.
Hayward and Kanter both fit around Carmello and Rondo very nicely. Both can play P&R, both don't need the ball, Hayward is a decent defender, and all Boston would then need would be a defensive C.
The big key for Boston would be getting rid of bad contracts. Their starting five would look like this:
Rondo ($13,000,000)
Hayward ($11,000,000)
Carmello ($23,000,000)
Kanter ($6,000,000)
Sullinger ($1,400,000)
That is $54,000,000 for your starting five. They would also keep Brandon Bass, Avery Bradley, Olynyk, ($13,000,000) which would put them at $67,000,000. That is a little over the cap, but they would still have some exceptions to bring in some more vets. It's a tight fit, but Ainge has done it before. I think that team is immediately top 3, and if LeBron decides to stay and Wade doesn't come back or Bosh leaves, who knows, Boston could win it all.
What would have to happen on Utah's side of things, would be they would have to take back salary (Green and Wallace). That means the trade would look like this:
Green ($9,200,000), Wallace (10,100,000) and Boston's #1 for Hayward ($11,000,000), Kanter ($6,000,000). Boston would still have picks in this draft as well.
Utah would take on 19,000,000, but would get two top 10 picks, and would still only be at $58,000,000-ish with this team:
Burke
Burks
Draft Pick
Draft Pick
Favors
Green
Wallace
Evans
Lucas
Gobert
Garret
Thomas
Clark
That's 13 players right there. They could then make some decisions on how to proceed with their mid-level exception, vet mins, DL guys, etc. They could easily decide to go young one more year, and go with the above team giving the young guys lots of minutes and losing a lot of games again, adding another top 5 pick to that team, or they could decide to cut loose a lot of the scrubs and add another vet or two and have this be our core.