I have only a limited understanding, but this sounds to me like a possible implementation of the TruthCoin idea. A sportsbook concept is essentially a binary prediction market. Assets can be created, such that instead of being pegged to a real-world commodity, they can be pegged to the likelihood of a certain event occurring. The likelihood of an event occurring has a fixed range, between 0% and 100%.
Looking at TruthCoin though, to me the specifications look way more complicated than it needs to be, with introducing a whole nother 'proof-of-work' CashCoin, and VoteCoins,...etc. I'd like to see if this could be implemented more easily in the bitshares framework with DACs. There are still many considerations and pitfalls to avoid (make sure the right consensus is always reached, and winners can always cash out), but just reading through that TruthCoin whitepaper it seems to me that this could be done much more elegantly.
The DAC of course could reward people for taking positions through transaction fee dividends.
Also because the asset has a fixed range, it would be possible to implement in such a way that holding extra arbitrary collateral would not be required. Long and short positions would have inverse costs. (If a trade agrees on a 0.3 price, then the long trader needs to risk 0.3 of whatever currency and the short trader needs to risk 0.7. Neither the long nor short position would be able to lose more than their original investment.)
This concept of course could be applied to any prediction market, not just sports. Politics are always popular, like a decentralized version of Intrade.