On their blog AdDuplex has announced their plan to turn into a proper advertising marketplace where developers can be matched up with advertisers, a bit like BuySellAds does for blog owners.
A developer you will be able to apply to AdDuplex Direct and have a listing for their app in the AdDuplex Direct Catalogue. An advertiser you will be able to browse the catalogue, select the apps they like and initiate advertising deals. When both parties agree on the scope of the deal the advertising campaign starts and when it’s over the developer gets paid.
AdDuplex would take care of the catalogue, ad serving, and money handling, and will take an 18% commission on the sale.
All Windows Phone 8 apps running AdDuplex SDK v.2 are able to apply, though initially not all apps will be included in the trial and only incorporated developers and not individuals will be accepted. Apps will also need to serve at least 10,000 impressions per day. If not enough ad inventory is available the ad space will default either back to the normal cross-promotional role or become hidden.