I think the Noel trade has officially left the barn. With Embiid's injury history and their insistence on trading Okafor, they essentially can't afford to trade him anymore. Maybe it can be revisited in the offseason.
But the more I think about it, I'm not sure how realistic Nerlens Noel ever was. Look at Brad Stevens's system, it's highly highly based on spacing...if you're a big man and you can't provide even just a threat of shooting 3s, Brad essentially doesn't really have a use for you. Look at all the big guys on this team right now that get playing time...Horford, Amir Johnson, Jerebko, Olynyk...all these guys, on different levels, provide SOME threat beyond the arc. I'm not even sure Noel has ever attempted a 3 in his career, it's just not his game.
That's why I think a guy like Serge Ibaka is much more realistic in terms a guy who Ainge would go after that could slide right into Brad's system with no real issue.