Didn't someone do this with Twitch Plays Stocks? Essentially gave them some capital and let the chat decide what trades to make. They nuked the portfolio within 24 hours.
Set up a system like that wrong, and it doesn't matter how smart the crowd is, you're going to lose all your money. It would be interesting to play with the parameters of the game and see how results changed. (how often trades are made, max portfolio % per trade, voting mechanics, etc.)
You'd want to play to the 'wisdom of the crowd'.
Perhaps some kind of voting on a selection of likely stocks?
Maybe introduce sales after it's been around for a year. (Though I'm not sure which mechanism, DCA doesn't work in reverse.)