It would be great if the next implemented airplanes would be the following:
Small Stand Aircraft:
Piaggio Aero Avanti P180
Cessna Citation X
Also those buisness planes could be both GA and commercial flight
Medium Stand Aircraft:
Those would add some different looks to the airfield, because all those variations of boing and airbus are of course important and should be added, but in that look from above in ACEO those would look mostly the same ;).