Size, Resources, Technology and Stability (political & economic) are in my opinion the factors for national power.
The USA tops in 4 categories - so I cannot understand why anyone would think it will lose its super power status, temporary mismanagement aside.
Russia has the first 3.
China has first two.
Japan, Germany, France have 3 & 4
India and Brazil have a secondary position in 1,2 & 3 and good 4.
Australia has 2,3,&4 but not 1 (not enough people!!!)
Objectively speaking all these have a chance to become more powerful than they are today but I just cannot see anyone topping the USA.
China & Russia - if they manage to usher in a better form of government can challenge the USA; otherwise they will continue to play secondary but powerful influence.
India will need some scientific miracle to be a super power in that same sense as USA. But then like in so many other ways, the Indian sense of super-powerhood will be very different from the rest