My take on those.
Rosberg is a maybe. I think he can do it and emulate Damon Hill, but he needs a good enough car to do it. The Merc won't do it against Red Bull and Vettel.
Pérez can and WILL win the world championship in my eyes. He I believe is at his prime or well before it, and he can do it if McLaren get their act together.
Grosjean? I question why you say him, as he is either fast and erratic, or slow and consistent, which won't win him anything.
Sutil is up my list of future champions as well. He is fast, consistent, and this would pay off if he was bloody more luckier than he is now. Hell, he may be one of the unluckiest since Chris Amon.
The Hülk can do it, but he needs a better vehicle. I think he can get into a Ferrari seat if Massa leaves, so who knows. Alonso plans to retire from F1 after driving for Ferrari, so he can be propelled into lead status if he goes to Ferrari. I thought he was a very good driver at Williams, although he got frustrated easily. I think he has matured quite a bit since then, so we'll see what happens.
I don't think Maldonado is a pay driver, I think he is good, but the fact that Bottas seems to beat him regularly and qualify very well tells me be is so etching special, but he needs a better car to show his true potential.
Bianchi is a definite yes. Considering he finished 13th on merit in Sepang, a track which I don't believe he has ever been to before, beat his teammate by over a minute, and has beat him regularly when he finishes, he can do something. If he gets a top drive, then he will win in my eyes.
In the 2012 Rolex 24 at Daytona, Felipe Nasr jumped into the Michael Shank Racing #6 prototype and he took off. He was on a hell uva stint to finish in a mighty impressive 3rd place on his debut. I knew he was something special when I watched him. He was very fast and consistent, which only certain racing drivers have. As a future champion, I believe he is one.
And who is this Harvey guy you speak of?