The current Glowforge units do use the depth sensor and measure height at a single point
The problem will be that the software doesnt fully correct for lens and perspective distortion, and incorrectly transforms points from the lid camera source image to x and y points on the bed.
Lens distortion will be fixed, but perspective distortion will vary depending on the height of the material. I’m surprised they don’t use the macro camera for scanning traces, since it would allow you to compensate for perspective distortion even on uneven materials, but maybe that’s a future improvement