Hey DM Dudemeister, I just thought I should thank you for this very cool idea. Your topic was a great inspiration to keep my PC's kingdom challenged in Rivers Run Red.
Since the Narthropple Expedition encounter more or less implies there is another Kobold tribe in the Narlmarches, I made them thralls of Hargulka's kingdom, scouts and skirmishers for his army.
I really liked the idea of a monster kingdom ruled by trolls, so I gave him Hobgoblin soldiers as well. I'll have them raid the PC's Kingdom and ambush merchant convoys crossing the Slough for slaves and loot.
Thanks for sharing your ideas again !