Re: Dr. Strange
I think the best indicator would be how willing Viggo would be to commit to a multi-picture deal. If he's willing to throw his lot in with Marvel for the next few years, then yes, he's signed on to be a major hero like Dr. Strange. But if there's no proof that he's going past one (if any) film, then I tend to believe Marvel is just following their formula of hiring major actors to play one- or two-shot villain or supporting cast roles.
THE COTTON AVENGERS
...They move like slick cotton on oil.