There seems to be a lack of French in your list Randall. Good as the existing Airfix set and the new Pegasus sets are there are still some gaps which need to be filled. The 37mm gun and trench mortars would make a nice start, but we could also use Schneiders and St. Chamonds plus some early and late war horse, and possibly Alpini and colonial troops. Heavy artilery would also be nice, but that is probably pushing it.
However like Malcolm I'd prefer not to see any one period, even one I am doing, be the sole period for a period of time.