Alright, can somebody think of a bunch of type weaknesses, resistances, and so on on that new "light" type? And also can anyone think of good moves for that type? I honestly doubt anyone can think of all that.
Unless someone can I don't think adding that new type is a good idea.
But there is one thing I don't understand. Why are dark types immune to psychic moves? Psychic is like magic, and last time I checked you can use magic to fight darkness. So I don't really see how that makes any sense.