100% cotton and a poly/cotton in the same quilt wear out differently and the seams are quicker to come apart between the 2 types of fabric. Now I am not talking in the near future but a good number of years down the line you will begin to notice the differences. There is no reason that you can't hold, keeping them separated and making i quilt out of the poly/cottons of their own. Mixing is just not a good idea.