Very good to hear and very reasonable. If you personalize some third party airports (besides your own), will those cost additional fees or will they just be added as one of those free updates?
It depends on the level of customization needed:
something that will just fix the most obvious problems like, for example, telling GSX which parking have fake/static jetways, we'll release it for free, because the whole point of GSX is that you don't have to pay to have an airport "supported", since it will work anywhere.
A payware level of support is something more involved, not just having an airport supported, but more likely packs of many airports together, grouped maybe by areas or by developer, with ground vehicles placed in custom positions for every single parking and also new 3d models and textures specific for the airport.