It's difficult to predict who the new superpowers will be. Most likely that will be decided by who can best weather market turmoil, as opposed to older metrics that heavily prioritised hard power, ie. naval strength, nuclear stockpiles, and troop numbers.
While hard power will always play an important and necessary role in international relations, it was through flawed economics and undemocratic practices that the Soviet Union collapsed, not a severe inconsistency in military strength. Japan was once considered an obvious candidate for superpower status but prolonged economic woes have left that an all but forgotten piece of trivia.
Among the more modern examples of potential superpowers, we're already seeing the very real possibility -at this point nigh-inevitability- of the EU at least partially dissolving as a result of today's economic turmoil. This is on top of the fact that the EU lacks a unified foreign policy and does not project its strength abroad with any sense of cohesiveness, either in economic or military terms. I think it was, at best, always going to be no more than a powerful trading bloc. In the foreseeable future, even that is out of reach.
It's difficult for me, personally, to picture Brazil truly expanding into the energy superpower that some analysts have predicted it may become, but it can't be denied that the country has shown surprising economic strength and has been taking steps in that direction, developing nuclear power and even purchasing an old Clemenceau-class aircraft carrier from France in 2000.
China, considered for many years now to be the front runner, has very real concerns that its economy will one day collapse into a black hole that will ravage the global marketplace like nothing we've seen before and quite possibly politically destabilise the country and region at large. It also has to worry about being checked on two sides by rivals India and Russia.
India, who I personally have been rooting for all along, has been developing a more information/tech-based economy, as opposed to what's been called China's "happy meal" economy. The basic theory is that as the global marketplace develops, there'll be an increasing demand for the sort of industries and products that India has been making a concerted effort to gain a foothold in, whereas China will flounder because it'll still be providing that more common, lower class of goods. India is also the largest and among the most diverse democracies.
Russia, on the other hand, has been making overtures about returning to its original prominence. This, however, would be on the backs of its citizens and probably quite costly to the world at large, seeing as how they would have to primarily lead with their intact military apparatus as opposed to any special character of their economy or their politics. Of all the possible candidates, I would like this scenario the least because I feel it would retard the progress that could be made in the 21st century with regards to the spread of liberal democracy and the reduced role of the world's militaries in projecting strength.
We're just going to have to wait and see. It should be good fun, regardless.