Custom NPC's are cool, but we really need more slots. Frankly, each custom NPC purchased should come with its own slot. So you "slot up" as you purchase them. This slot imo though could also be used with mounts or non combat pets. Think of this as the same thing as the pack rat or pig that give 5 inventory slots. You get a pet and function. How about Houseguests come with an NPC slot, so you get a pet and function.