I don't think they create Pokemon to fit a certain type, they might say "We need more Steel types" and create some based off of that, but I don't think they're not going to say, "Oh, we can't have this be a Pokemon because we don't have a type for it." Porygon's line would be a perfect Digital type, but in the end it's just normal. If they create a "Light type Pokemon" what's stopping them from just making it a Psychic or Normal type? I don't think that not having more types is limiting their creativity
Maybe if they gave Poison a bunch of super high powered moves instead of adding a new type? idk I just think that adding a new type will fix anything.