Doug,
Here are a couple of thoughts...
On my classical guitars I have a depth of 95mm at the end block and 88mm at the heel block. These measurments are without the top and back thickness which would add approx another 5mm to the overall depth of the instrument. You would be adding another 12 mm. roughly to each of these measurements plus then the back and top thicknesses. In my opinion this is a bit much. I can't recall ever seeing one that deep but most of what we do is educated guesses anyway. Who knows , maybe you will start making deeper instruments and in a few years everyone will be copying you.