The two that you haven't mentioned in your potential list are the United Kingdom and Japan.
Japan currently holds the 3rd position in terms of economic rankings (although this precludes the EU) and the other advantage they have over other countries for the future is that they are currently still investing heavily in scientific research. There are some fields of physics in which the only research jobs in the world are located in Japan. The downside is that at present they have a declining population (actually negative population growth) meaning that their numbers may not support their economic goals for the future at some point (although this is doubtful to manifest as a real issue in 32 years).
The UK is reasonably high on the list and the loss of its economy to the EU will be a blow in some regards. It is completely dwarfed by the combined economies of the EU of course, but it currently sits at 5th in economic rankings but has been dropping. It is less likely to be a power going forward unless it reverses this trend, but it may well do so in the future. Its success was largely based on military technology sales, but the USA has dwarfed its capability in that regard for some time and it is looking for other areas of development now. I don't know enough about how this search is going, but if it finds a good niche, then you might just find it on the rise again. The people of the UK are generally unafraid of hard work to achieve such goals.
Given the ever increasing population size, some commodities that we take for granted now may well become even more important than technical wares into the future. The obvious ones here are food and energy. If food becomes the 'new oil' insofar as it becomes the most important commodity for global trade, then one country that's not currently in the race may well rise;
Hear me out on this one; Australia exports a lot of minerals, yes, but it also exports a lot of food. It has a far greater capacity to grow food than it has to consume it and this could easily make it a superpower in the future if the need for food increases. Additionally, Australia is more or less the 'Saudi Arabia' of uranium, with around 30% of the world's reserves. If nuclear power for all those people suddenly becomes the norm, then Australia's rise as an economic superpower is assured. It's already investing in higher learning, with tertiary education now being its third highest export. All we'd need now is a solid research program and we're set...