I don't understand Boston's decision making process here if the rumours are true.
With Brooklyn's unprotected pick next year, they have a good shot at one of the bigs.
Fultz's and Thomas' tendency to score, while still being capable off the ball are going to work well together. Fultz is also a good insurance in case they realize that Thomas + Horford is an impossible combination. Getting more assets back from Philly means obviously more chances at landing stars long term, but it's also a risky gamble in case the team they get the extra assets from (Lakers, Sixers, Kings) improve.
For the Sixers I don't think Fultz is a good fit. He wants to touch the ball, his playmaking is not based on passing or off ball movement, the biggest threat is his scoring potential. Simmons and Embiid project to control the ball for extended stretches as well. As long as Simmons is a non shooter this limitation will either shrink the floor or make him the primary ball handler at most times. While Embiid is not the optimal partner for a 4-5 PnR, his shooting makes him an option off the ball or an dangerous off ball screener, who can be involved in staggered screens, and either cut for lobs or fade out and shoot/attack the close out/open up the zone if the rim protector follows him.
The question remains the same: How is Fultz gonna fit if he can't touch the ball or has to navigate a lot of traffic all the time?
One option would be a 1-4 PnR heavy system, where Fultz and Simmons are the main factors, while Embiid uses his quickness, length and athleticism to terrorize the defense with backscreens for Stauskas and RoCo. Stauskas is improving on the catch, he's still more comfortable as a 2ndary ballhandler.
The Fultz + Simmons PnR would revolve around Fultz's 3 ball and versatility. Any confusion when it comes to switches and help will either nix Simmons limitations and let him attack the basket or Fultz will have extra space. I'm still not convinced it's wise to bank on that, when Monk is basically the perfect fit to play alongside Simmons and Embiid when taking him also means more shots at drafting good guys in '18 at wing.
Guys that are willing and capable movers off the ball are really undervalued IMO. You only have so many possessions and too many cooks tend to spoil the soup. The Heat never could fully utilize Bosh offensively, because James and Wade had so many touches. Same is happening in Cleveland with Love, some of his biggest strengths are only there in theory. Steph's and Draymond's touches went down in Golden State when Durant came. Steph finally figured out which possessions to take and where Durant's length was superior to his skillset, Draymond doubled down on hustle and defense. Klay is just running around and the threat of his catch and shoot is stretching the defense without him touching the ball. Monk could do something similar around Simmons.