There are strategies to do this now, but they're hard to execute. One example is to target stocks that are likely to enter or drop off indicies. Index funds will be looking to buy or sell them soon.

Mostly these strategies depend on your ability to set up a very high speed link to the computers that clear trades and interpret the algorithms that index funds use to establish their samples of the market. If you can get in just ahead of the index funds and their monster volume, you can shave a few tenths of pennies from the investors.

You can make millions with those strategies but it's a drop in the index fund bucket. Quite a lot of "quant" trading activity is about ripping off ordinary people by unnoticed fractions by getting in ahead of them. Much more innocuous than the large scale bribery and fraud that makes up so much of the financial industry.