Idea for a new fund directed at retail investors:
S&P 520 index fund. It's basically just low cost S&P 500 index fund, except that the index tracks 520 largest companies listed and individual investors can remove any 20 companies from their index. If you don't know what to drop, the fund managers drop the 20 smallest and the index becomes S&P 500.
The catch is how to implement this strategy with low cost. In practice the fund as a whole would take input from every fund owner at the time they do rebalancing. Then they would adjust the ownership of the fund based on how the investor performs relative to the whole fund in the next rebalancing. How to implement this may be tricky.