An economic system that concentrates wealth will prove to be unstable in the long term. With the rise of robotics and computing, there is potential for massive unemployment and huge economic disparities between the investor class and the working (but now unemployed) class. A major change to the economic system is inevitable. If the needs of the population are not met, civil unrest is likely. If the needs of the population are met, extreme and unpredictable inflation could disrupt markets, or even some sort of parallel currency based on human time could arise. If investing is still possible, the returns will be much lower.
The world economy will undoubtably be different in 500 years, but there's no reason to expect markets to stop functioning. Space travel, technology and medicine will all require private investments, and investors will continue to see returns as they have since the beginning of corporations. 4% annual return (above inflation) seems much more likely than the 2% prediction; a carefully managed fund like the Foresight Fund will very likely continue to deliver in keeping with its historic returns.
$1000 at 2% real return would be worth $19,956,569.14 in 02015 dollars. If the Farsight Fund returns more than that after fees & taxes, the challenger wins the bet.