Is it really a fact that Boston needs a big? I feel like the move is just Horford and Rob splitting time at center and Boston playing more Derrick and Grant. Kornet and Muscala are fine as cheap regular season bench guys and you just manage minutes to get everyone to the playoffs as healthy as possible.
Turner/Sabonis/etc can't guard Embiid anyway, so I don't think I'd want to dedicate significant assets to a marginal move.