For the capture itself, and while it’s not quite what you describe, I did a little experiment back when I was obsessed with X/Y belt calibration, with an arduino acquiring the digital output from a cheap caliper.
I imagine one could do the same with a digital dial indicator, that you would drag across a surface (sounds scary…and would only work for wavy/continuous surfaces)
After collecting the data, it all depends on what you want to do with the mapped surface ? The main value I see is what is shown in that EstlCam video, i.e. carving/milling on a curved surface.