I wouldn't have a problem making things like a C5 galaxy, but here are the problems with me making one:
It is really large, and Blockland wouldn't handle that well. People would spawn them in the bedroom and kitchen.
Torque collision is bad and it would glitch through bricks and would only work on flat, long surfaces like slate or some huge airport build.
The majority of Blockland players have a hard time grasping the ability to type the words "You, Please, Thanks" and various other small words and phrases, I doubt they can manage to take off, fly, and land that huge plane.