Honestly, the best kind-of player the Sixers could trade Embiid for is a guy like Kemba. He is great on or off ball (allows Simmons to be himself), can score from anywhere (won't clog up the floor), and is an excellent locker room guy (not that Embiid isn't, but, come on).
I understand this kind of trade would never happen - and I don't even think I want it to, even given the apparent value disparity - but if I were Philly, I would look to move Embiid and not Simmons.