Is it possible to display the cutting path in 3D in QTPlasmac?

Not sure how things work regarding the Z-hight in plasma so I'm not sure this is a valid solution for you:

Presuming a pipe diameter of 150mm you would need to change the cutting hight from Z0 to Z75 in the gcode then you load the gcode with work offset in y,z= 0 (MDI: g10 l2 p0 y0 z0)
this should give you a correct preview of the path.
Then to get a proper live plot you need to set the work offset for z = half the pipe diameter (MDI: g10 l2 p0 x0 z-75) Note you could also have an offset in X here if you wanted.

This is the result I get:
 

I'm afraid that is the best solution I can come up with for the moment.

Also for future reference:
Currently there seems to be a bug in the A! rotation code in the sense that the z work offset is only interpreted in inches. Users working in inches can load gcode with Z height set to zero (Z0) and get a proper preview and liveplot by setting the z workoffset to 1/2 of the pipe diameter.