It really is not a problem at all mixing washed and unwashed fabrics in a quilt as long as you do a reasonable amount of quilting, since all of the fabrics will conform to how the batting shrinks. A fabric that shrinks a lot when washed alone will not shrink in the same way when quilted. Shrinkage differences from mixing washed and unwashed fabrics in a tied quilt can be a problem because the ties are not enough to "bind" the fabrics to the batting.