With polls already existing a betting system could be brought in. A rough idea on how it could work -
A and B streamers are in the same team of a call of duty match and they start a poll (bet) on who will finish the match with more kills and viewers can bet on their choice of player ( A or B ). For eg. a 100 people bet 1$ each (preset odds are 1 for both) on this poll where 60 chose A and 40 chose B. B ends up winning the bet hence the voters who chose b will double their money while the people who voted for A will loose their 1$. The remaining 20$ would be twitch’s profit. In the same scenario if A won the bet, B would be liable to pay 20$. A bet limit amount could be set by the streamer
Twitch already has channel points betting, why would you need this feature with real world money?