Assuming a coaching change is not in the works, I think the best move for right now is to move Horford to the backup C spot. He's just not playing anywhere near the level that he's capable of (unless he's fallen off a cliff since last season). I would seriously consider starting Matisse at the 3 when he gets back, that has the added benefit of moving Harris to his natural position of PF. Until Matisse gets back, go with Burke. And I wouldn't rule out both of them in the starting lineup if things don't improve. But I think either of them would improve spacing (for both Embiid and Simmons) and ball movement once you get past the first 7 or so seconds of the shot clock.