I do agree that Weidman can put him down and will probably get the better of him from the top position, but I don't think it's nearly impossible for Vitor to get a sub. Do I think it will happen? Not really, but I personally don't think it's as unlikely as you're saying it is. Just my opinion.
Weidman has good defense standing, but he's never fought anyone who can chase as well as Vitor. This could make a very big difference in the fight. Vitor's style is not as technically sound as Silva's but the explosiveness of it may catch Weidman by surprise.
Chael presents an interesting match-up. He's very tough and would definitely be the best wrestler Weidman has faced in MMA, and also has great cardio.
It would be interesting to see what Weidman does if Chael could get him on his back.
I think Weidman would win early though, probably by submission.
Personally, I'd rather see Weidman fight Rashad Evans (if he moves down).
I've only seen one fight with Romero, and I thought he was entertaining. I was impressed with his cardio. His style was very active and it just about went the distance, yet in the post fight interview he wasn't breathing heavy at all. I'd like to see him fight Uriah Hall.