It's a neat idea but, as far as I can tell, it's still a still camera.
Yes, I know that many high end (and some medium price range) digital still cameras can shoot in cine mode but, no matter how you dress it up, it still quacks like a duck.
A lot of digicams that I have seen which can shoot movies have certain artifacts like "rolling shutter" effect where the picture breaks up or skews sideways when the operator pans from side to side. It's also a lot more difficult to control exposure, frame rate and other things on a camera that is primarily designed for stills. That all begs the question of how you operate it different modes or record sound when all the controls and inputs were designed for stills, as well.
I think cine mode in a still camera is a neat idea for occasional use but, if you want to shoot movies and do it right, just get a movie camera.
That, having been said, there are all kinds of shoulder brackets and rifle stocks on the market. Many of them have remote viewfinders and controls that are similar to yours. Why not just get one from a commercial manufacturer that you know will fit your purpose without all the mucking around?
It's still cool. I'm sure you could make one, as you say, out of furniture grade plywood which would work just as well. Plus you could customize it any way you like.
I've always wanted a real rifle stock for my camera.