Why should they? Look at how many people are actually Wood King or above, barely any. Until that number increases there is really no need to add any new ranks..
Whats higher than king in real life? It would go past the original idea and even if there was more, you'd have to keep making more. Carefully considering what you are naming it cause it'll probably get passed.
I think that copying COD would be weak and well hated. Maybe more in-between ranks and a couple more perks would be nice. I'd need some help with the Perks one, though.
Make wood and iron further apart, or iron and gold closer together. It jumps from a 5k point gap to a 25k point gap. Gold is more than twice that of wood in your numbers!