At the moment ad networks perform internal auction models in order to deliver the best possible value to the site and to the network. This technology is why some of the larger networks have been able to enter into CpA deals. Optimisation takes place on the network's servers, with little or no input direct from the site.
The new system will allow sites to be a member of more than one network at the same time. This will allow all the networks to extend their reach, but at the price of making generic network activity more expensive. The question is whether this cost will be absorbed by networks or passed on to advertisers.
I suspect we will see networks offering adantages to sites that sign up to them on an exclusive basis. Content aggregation along the lines of the Washington post's blogrolls or the UK's newly launched messagespace will allow advertisers to find ways to speak to targeted audiences, while networks will allow broadcasting.