I came across this short video showing a guitar that adjusts the string height with a key. I've never seen anything like this. In the comments it is mentioned that some 19th century Russian 7 string instruments and the Stauffer instrument adjusted their instruments in this way. I wonder if this would work on a steel string instrument.

https://www.youtube.com/watch?v=djpKl_3lZnA

 Interesting. Thanks for sharing. I'd heard of it but not seen it.
After seeing it, adjustable neck height is a hard pass for me. I want more resonance between the body and neck. Notice how the neck joint is a cavity? For the mating surface to be able to slide with use of a key means there must not be a whole lot of pressure between those two surfaces. I wonder if this would even work for steel strings or if it would add a lot of weight because they can't use a traditional neck joint. Adjustable bolt-on necks work because they are seriously locked down. But, IMO, nothing beats a traditional dovetail and that's what my favorite guitars happen to use.

 Once I cut a saddle, I'm done and never have to think about height again so this would be a big down-grade for me. BUT, I can see a touring musician who has issues with action and stability maybe considering it.