I don't think Weidman is unbeatable by any means or that he is even the next great champion, however I regard his composure very very highly. For that reason I don't know if Machida's unpredictability will necessarily be a huge advantage for him against Weidman should they match up.
Weidman has learned so much from even the 2 or 3 total rounds he had with Silva, that experience only enhances his already exceptional composure. I don't think he'll be phased that much with the Machida style. Weidman has imposed his will on every opponent he's faced and he's outstruck every opponent he's ever faced.
Machida's take down defense though is something to consider. That is a part of the fight that nobody can really predict. Moving down will also probably bolster his take down defense, even against a big middleweight in Weidman.
I just look at Vitor's swagger right now and the way he's finished his opponents, he seems possessed. He's also a big middleweight so Weidman perhaps will have a bigger challenge in overpowering him and keeping him on his back. I just know you're going to get a balls out effort from Vitor, he's going to leave it all in the cage. With Machida I can't honestly say that. It's not necessarily a bad thing for Machida, that is just how he fights.