The light type that many fans have sought over the years is nowadays supplied by a combination of fighting and fairy, the first being the "good guy/hero" type and the later being the "pure, magical" type. Both combined give the idea of "good" vs evil (the dark type), which is more or less what light is intended to be.
I like to think that normal type is in a way, the closes to the sound type that we'll get. I mean it has boomburst, sonic boom, hyper voice, etc. Sound being a category for moves rather than a type itself is a good thing to me, as it allows to have sound moves of all types instead of all moves that use sound belonging to the same type.
I see fairy and psychic as "the cosmic" type. Fairies are tied to the moon and psychic is tied to celestial bodies, space, aliens, etc. so with both around a cosmic type is not needed IMO.
The only types that I would be interested in seeing introduced would be a rubber/plastic type, for the lols, and in the case gamefreak had the balls for it, fuse ground and rock into a single type, the earth type.
