The only way he makes sense for the Sixers to get Harden is if the can do it without including Simmons and Embiid. That is a hard trade to pull off, but you'd have to move Harris and Horford, not sure Houston would want either of them. If they could do it without moving our big two, Sixers are the better fit. Simmons is at least as good if noy better facilitator than Kyrie and a far better defender, and Joel is just a shade less offensively than Durant (assuming he is back 100% from his achilles injury) but he is a better defender as well.
In any case, I would not be surprised if the Sixers stand pat and try to build around the edges, but Simmons, Embiid and Harden would be fun to watch, and they would be instant favorites, not to mention, it would be a more attractive destination for veteran minimum players to choose the Sixers.