GSX in its current form can't be released on the MS Marketplace ( PC or Xbox ), because it requires an external executable to work, and those are not allowed on the Marketplace. If Microsoft will eventually allow .EXE file in the Marketplace, which has never been confirmed as a planned feature, it surely won't be for Xbox anyway.
We are considering a Lightweight version that will work just a Ground vehicle model replacement product but the main issue are replacement Jetways, which would be one of the main features, and their management also requires an external .EXE to Disable/Enabled GSX Jetways on selected airports and, because such app would require accessing the filesystem even outside GSX own package, to recognize 3rd party sceneries, and that won't be allowed as well.