As far as I know, the opening of new betting exchanges is an unpromising undertaking, as even the No. 1 in this business (Betfair) still has problems with the liquidity of many markets.
The main problem is traffic. No Peer to Peer site is going to have the traffic like on a normal sportsbetting site. Its because the site with its own bank roll can offer more bets/odds. Where as in a peer-to-peer system you need to find someone willing to take your bet. Apart from that, you will also need all those people on that one site. There are already a few like wagerr, who even launched their own site and integrated the whole system in their wallet, but literally have no volume from last I visited.
So the problem is that it is a problem for any site to get good traffic. And for a betting site, this is generally a difficult task, since there is a very strong competition in the market and players choose well-known brands in the first place in order to have a guarantee for the payment of winnings and the safety of their money.