Are you saying you want to do it with comments? A custom DApp front end might be better, if not a bit more difficult to create. You could get the trading numbers from Yahoo or another platform with an API, then have users make their predictions through that.

I could see a trading game dApp being fun...but it's all in how you make it. Hell, I don't even know if I'd do that well, and I trade every day. Because I don't really make bets on crypto being a certain number or whatever. I just put in sells and buys based on what the charts look like, always hedging my "bets" and never really trying for maximum profit. So, if a game were based on a certain coin or stock hitting a certain point, I might do horrible. But, I still manage to make regular "profit" in the crypto market.

As to the whole wisdom of the crowds thing...I have no idea how that will work out...

But I hope if you do end up working with someone to make some sort of Dapp trading game that it's fun.

Or maybe it would be similar to trading, just maybe a bit more like betting? I dunno...I didn't follow everything I think.