[audio:http://www.withinwindows.com/files/uploads/2011/06/06202011.mp3|titles=Short: Windows Phone Mango blocks "Interop Services" apps] With the Windows Phone Mango embargo having expired today, I can now mention Mango won’t officially support the deployment of custom applications with the ID_CAP_INTEROPSERVICES capability flag. This undocumented switch was used in WMAppManifest.xml to enable access to a COM-based platform interoperability bridge, between managed and unmanaged code. This bridge powers many homebrew and mobile-operator (MO) applications today.
Some quick research suggests this limitation is imposed only at deployment time, to maintain MO application compatibility, but further analysis is required. With side-loaded applications not requiring a digital signature, my first thought is to perform runtime manifest modification. YMMV.
For those curious, deploying an application with this flag in-place yields the error code 0x81030120.