Respected Sirs and Madams of IPC,
I personally believe that no matter whoever ascends to the throne, the USA will never recover from its economic, political and military setbacks. With a huge level of debt ($18.5 trillion), it will take at least a 100 years for the USA to clear it off. China is fast marching and will surely become the future superpower. Some of its power is quite flawed. A crashed real estate signaling a weak currency, excess corruption and a restive countryside where tax collectors are murdered regularly. But this is compensated by their massive military and the new kinds of weapons (like the Wu-14) that they innovate and develop further.
But I personally believe that China can't maintain that position for too long. This is because China doesn't have energy resources within the country. They have to rely on the Gulf, Iran, Pakistan, South America, etc. for oil and natural resources. And no country maintains its monopoly over any other country forever.
Japan had far more powerful secret weapons than the USA during WWII. But the lack of energy resources due to the USA's cutting off of Japan's energy route hampered Japan's juggernaut. Japan and Germany, which were otherwise pulverizing the USSR, got crippled, and by 1943-44, both nations were nearly out of reliable conventional military hardware and energy. China today, having realized Japan's loss, has sought to pursue energy resources with vigor. A very smart move indeed.
But China cannot maintain their superpower status for long, due to the mere fact that they become dependent on other nations for energy. I believe Russia, which has abundant natural resources and the world's most powerful military, navy and air force, not to mention vast powerful biological, chemical, nuclear, scalar and secret weapons, will be a better candidate. If not Russia, it will only be the IRI.
As of present, I don't see the IRI faltering anytime soon. It will grow stronger and stronger as days go by. By 2017, IRI will be a followup superpower to China, which will surely become the sole superpower by the end of 2016, with the USA becoming a junkyard for Chinese products. Europe will turn insignificant. Only Australia/New Zealand will be up and running, despite not being major powers.
To summarize: If the USA is to be replaced by another superpower, which is very soon, my sure bets are on Russia. If not Russia, the IRI. China is a definite contender but has a lot of flaws and corruption and a lack of oil and energy resources that will make it more dependent on foreign nations. China will hold on for a while, but not forever.