It's a difference between setting a standard for Passenger / Cargo planes (they are defined in the aircraft editor) or a individual type of plane like the Airbus, the Boeing 744, 777, 787 or whatever.
But in another topic, Umberto said they consider adding the possibility to add the Number of Crew and even if they leave the plane into the Aircraft.cfg. It will come, I guess, just not that close by.
In the meantime, FSLabs, Aerosoft and others are already working on implementing that.
The other problem will take longer for sure. As Umberto said in another topic: It's not easy to fit people in smaller planes. You need a complete new set of people and animations for that. You have to define not only the floor, but also the roof of a plane and still the movement should look real, thats not easy to acchive in a simulator. You have to keep in mind, that Prepar is not developed for Animation of people... So, I am not sure if it will come. I am sure they try to make it possible. But that's a hard one to develop.