>>379892825
It might not be that bad since you're shifting it an extremely tiny amount, especially if your screen is already very high resolution and tiny. The fans might even produce more vibration compared to the wobulated displays, and Cambria has two. I'm sure they could make it robust enough. Mechanical varifocal on the other hand seems much more difficult to engineer robustly. 

Also I did only mention the mechanical method but there is a "solid state" method the other anon mentioned. To explain that concept, you can basically think about it as a special type of lens that does nothing when left alone, but then when you run electricity through it, the optical properties change. This can be used produce a shifted image.