The obvious answer is Embiid, but honestly if both Philly + Boston decided today to trade Embiid/Sully for whatever they could get for them, I'm not sure Philly would be able to get much more for Embiid at this point. Sully is not worth a heck of a lot in trade but Embiid's stock has absolutely cratered.
I think Philly could probably get a late 1st rounder for Embiid, but I'm not a doctor nor am I privvy to the "real" info, so that's just based on the idea that, as far as anyone knows, he might play in 2016.
I do NOT think Boston could get a late 1st rounder for Sullinger right now. If he had actually lost weight since last season, yes, but if anything he's even heavier. Not being able to get into shape for a competitive team in a contract year is a red flag that absolutely no one is going to miss.