VaLeo actually made something similar for a russian airport several years ago. You can find it at http://valeo.flightgear.ru/sshot/marshall/ and more info in the topic viewtopic.php?p=125510#p125510 Might be useful reference material.
I don't have time to test it today, but I do have some comments that I think are best shared early:
- your merge request seems to change the indentation, thus touching every single line of files like 747-400-set.xml. This makes it very hard to see what you've changed.
- scenery models and airport data (jetways, ramps) should not be pushed to Git, but directly to the scenery database. Git is synched with the scenery database (not the other way around!) before each release.
- your work won't make it into 2.12, as that version is frozen for new features as of July 17. This means that you can spend some more time to make sure it's done properly. Might make sense to wait for Hooray to comment on your Nasal code for example.
- did you think of placing the marshaller based on the groundnetwork? With the heading, center and radius of the parking spot, one could easily position the marshaller in front of the aircraft. Would be a lot easier to maintain than yet another data format. Aditionally it could be wise to see how/if X-Plane handles this. Taxi routes and parking spots are part of newer apt.dat formats after all, so we will likely go down that route one day.
Cheers,
Gijs