Well I guess the question I have to ask is how exactly are you defining "pusher axle"? When you say "pusher axle " to me, what you are saying is a powered axle that is connected to the driveshaft. However the picture you linked has what I have only ever known of as a "drop axle" which is there for when you frequently pull very heavy loads and need the extra axles to stay legal.
With the 1.14 beta that came out for ETS2 today we did get what I would call a drop axle. SCS has named them tag-lift, referring to a drop axle on the rear of the truck frame, and a mid-lift which has a middle steering axle that raises. With this new implementation I can see the potential for modders to made a 6x truck with an extra drop axle, but currently all SCS has given us is a 4x truck with a drop axle.