Since last week I have been playing with the new jetway feature of FsX, to see if I can get my own jetway model used in there. I still need to learn a little more about bones, skins and IK animations to get it all working on a proper jetway model, but tonight I learned a very valuable lesson.
If you are trying to use the GUID of a jetway model in the XML Jetway command and the objects do not appear, please make sure that the three IK handles as described in the SDK (IK_MainHandle, IK_SecondaryHandle and IK_WheelsGroundLock) are implemented in your model. If you use the GUID of a model that does not have them, nothing will show at all. So not even a static jetway. Took me a little while to figure that out.
Once I also got the animation working properly (only did some test IK animations until now), you can be sure I will report back again. But I am confident now that it will be possible to replace the default jetway model, with one that looks more like the real jetways on the airport.