Description of problem: If I create a service pack with multiple packages, I would like the ability to cherry pick a few to install on another system.
What's the use case?
One example: I create a multimedia service pack with a bunch of multimedia packages for both GNOME and KDE users and the users gets to choose what they want on the other end depending on the favourite desktop environment or I package alternatives of the same app - Eclipse or Netbeans and the user picks usually either but not both.
I don't really want to support this mode of operation. In your use case you would create two service packs, one for GNOME and one for KDE. PackageKit is complicated enough already.