I found this on youtube.This reminds of the pattern inside of shamisen which make me wonder what a dou made like this would sound like. The pattern would be visible on both sides which would be look neat IMO.
What do you think?
If I get it correct the reason to have it in shamisen is to reduce sound reflections from unwanted directions and reflect sound more to the front. (The efficiency of this solution is still under the question). On the guitar body IMHO it is only cosmetic, no more. It might make body a bit more rigid (more sustain) but it more easy achieved by the material choice, again IMHO.
Correction: I did not realized at first what it is just cosmetic, no actual grooves, just the pattern. Should look quite interesting on shamisen but again, traditions 
I was joking a little but it does look nice. Looks a little bit like a basket weave and would look interesting on the curves of the dou. If I ever get enough free time and plywood I’d give a try. If it did sound good it would be worth doing.