i'm curious to see what he does for the Rohirrim. Tolkein himself wrote he was inspired by the Anglo-saxons when he invented Rohan, but since the real anglo-saxons were not big on cavalry there aren't all that many miniatures makers making mounted saxons at all, much less in the kind of variety needed. and things like mounted Picts or late rome germanic tribesmen tend not to have a lot of armor on.
thinking on it, his best bet might be to kitbash, using gripping beast plastics with late roman/arthurian cavalry bodies, arms, and mounts, and then heads and shields from the saxon infantry set.