The impregnated marine plywood is supposed to be enough resistant enough against moisture. I agree that in the long run, it might not be a perfect solution. However, Tthis issue could be resolved by the Aarchitect or builder with a better sill design that prevents the plywood from direct contact with water. The sill that I see on their drawings does not seem to be appropriate. Tomorrow, I meet Gordon Sillars and will ask him to make a sketch that shows an appropriate sill.