if i had to guess why there are no screen shots.
its because they drastically altered the model of the trebuchet from the concept art. Like the case with the centurion its shoulders had to be broadened from the concept art so that there would be no clipping. they probably did the same with trebuchet and it doesn't look like concept art anymore.
considering the backlash after release of stalker models. and the nature of PGI to hide things. I wouldn't doubt that they decided not to show it because people wouldn't like it.
Edited by Tennex, 18 February 2013 - 08:03 PM.