I have noticed that the FS-Expo livery buses have disappeared from P3D - not sure if that is a coincidence or not. (see my post screenshot)
It hasn't. As suggested by other users, it has been assigned to appear ( randomly ) only at KLAS or KMCO. Users suggest, we always listen...
It would be good to be able to do the same with the larger passenger carrying buses also. These buses typically either have the Airport logo on them, and/or airline logo.
Everything will be good, and everything can be done.
But in order to be realistic, as you said yourself, the Passenger bus usually have the airport logo, and more rarely the airline logo, and most of the time this is DIFFERENT than the HANDLER, which is what GSX use. The other two are the catering logo and the jetway logo, which would be even less appropriate than the handling logo.
In addition to that, Passenger bus logos are usually full size over the body, which makes them more complex to customize without having the source files. And in addition to that, we don't use Photoshop for textures (that's not right in PBR), so we don't have the means to create a multi-layer .PSD that users might repaint.
That's an obsolete way of work, we now use Substance Painter almost exclusively, which creates multiple textures on the fly, using its own layer system that doesn't translate into traditional layered .PSD so a possible "PaintKit" for these full-livery vehicles, would require users to have Substance Painter installed.
That's if you want to have full covered liveries, which is how Passenger bus are usually made. Doing with the simpler Base Color + Logo approach of the other vehicles might be simpler, but it will still require to add a new customization class, some UI in GSX to it, etc.
At this time, we are more focused on doing something more substantial than this minor eye-candy feature ( the Bus is there, and it works ), for example adding new services like Emergency Vehicles ( we placed a static preview on Basel ), and ensuring compatibility with the next generation of Flight Simulator(s).
