UPDATE
Thanks to Aerosoft, which supplied me with a copy of their new A318/319 very quickly, I was able to add a proper GSX config for it. To get it, just run the FSDT Live Update now.
Be sure you remove any configuration you might have made/downloaded in the meantime from the %APPDATA%\Virtuali\Airplanes folder.
NOTE that, as usual with the Aerosoft Airbus, if you call GSX before setting the payload, GSX cannot estimate the number of passengers onboard correctly (since the airplane is still empty), which usually result in the wrong number of luggage carts and the wrong passengers bus called.
By turning off the new "Estimate passengers number" in the GSX Settings->Simulation page, you can now explicitly set the number of passengers so, GSX won't be confused anymore by any custom progressive payload simulation the airplane might have in place.