It isn't necessarily a moot point. The point to their types is that they are all super effective against one, and not very effective against the other. it's a perfect triangle which helps show how types work in regards to advantages and disadvantages, by making the three starter Pokemon equal. Them being equal also means that no starter Pokemon is really stronger than the other, so it's more of an even choice. A secondary typing of Psychic, Dark and Fighting doesn't accomplish what Fire,Grass and Water accomplishes. I never said it definitely will not happen, because it could, however, I'm saying that because it isn't a perfect triangle, I am doubting it will happen. Not that I wouldn't enjoy it, personally, I'd love a Fire/Psychic starter Pokemon.