Hello !
I managed to print a test "cube" with my prototype of scissor-z-axis FoldaRap 
More on the RepRap wiki.
Now that I reached this point, I kindly ask if it would be possible to implement this kind of kinematic in the firmware ?
Maybe independently of the XY choice as it could have been a Cartesian base with a scissor bed, or other combination (a core XY in my case).
As far as I understand the firmware part, the non-linearity computation could be similar to a linear Delta machine but simpler (solving one square triangle instead of three). This 2014 post in the RepRap Forum was about the same subject but was never concluded.