Thanks fuzzel for adding the z-scale! So when you say it’s going to take time you mean a few days rather than a few hours J Man, FarSight and the Pro-Pinball guys could learn something from your delivery speeds 
I just had a chance to test briefly and the z-scale seems to initially work well for one of the purposes I saw the most need and that was for the newer Hybrid Views that Rascal has been working on / demonstrated. They looked a bit compressed previously but adding a scale of about 1.5 nicely stretched it out without the disparity of the ball size not changing being a visual problem.
As far as the ball size, I imagine that indeed not having it alter is the only way to go as making it stretch visually (vertically) would not look right as it would no longer be a sphere and enlarging completely / proportionately would not make sense as the table is not getting any wider / taller when the z-scale is being set up above 1 (any narrower below 1).
I think values of 2 or above for the Z scale will likely not be practical for a few reasons but in addition to the 1.5 mark seemingly being a starting point for HV tables, the FS tables look like maybe setting at 1.2 and reducing layback could help provide some slight depth improvement. However, I think overall with FS tables it will likely provide more of a fine tuning option / ability between how much of layback to use and how much z-scale rather than radically opening up a whole new world of depth, which I don’t think still can be done too easily with the concept of filling all the screen and the general overhead view of FS in general.
To confirm, I imagine it’s just the visuals that are stretching and nothing about the physics (just like the X and Y scales). So even if the ball looks smaller, it would still be blocked by a wall at height 49, if using the standard ball size of 50, even if the Z-scale has been invoked, correct?
Lastly, I think that a little more depth even for FS might be able to be achieved if you could also provide a Z offset adjustment just like X and Y so you could set the perspective of the viewer / camera higher or lower along the Z axis. This should also help in imitating the varying height of a player from their perspective in front of the table. With also adding a Z offset function I think we could get a little more tweakability and would be cool to try out if not too much more work. Plus it would round out the settings screen so that all axis have a scale and an offset parameter – nice and symmetrical 
People will have to keep in mind if they use it that, as you say, the primitive objects will need their scale along Z altered as well and I imagine matching the value of the general Z offset. However, that seemed to not be the case with the 3D mesh primitives as they appeared to stretch from what I could tell from my brief tests whereas the native primitives looked like they stayed the same height and would need the Z values on the primitive adjusted (more testing on this item to come).
Thanks again for adding this and I’m curious if it’s a ton of work or a totally different arena for the Z offset option. Also, curious as to other people’s tests / findings.