Highly doubt Sound-type, it doesn’t really fit with other types? What would it be weak and strong against? It doesn’t fit very well at all, considering all the types that exist. Most type advantages and disadvantages actually make sense in some way or another. Sound doesn’t fit very well with any. Yes there are moves that are sound based, but as a type, it fits very poorly.
I don’t like the names Fairy/Light myself, but I am good with a new type, and can see Xerneas being the new type. I personally see something more doing with space, or something more spiritual, which I suppose Light works as a name in that sense. I have this all part of my old Sylveon analysis (which I should update) which you can see here. We have new information, that better suggests Light over Fairy too, seeing that whatever Sylveon is, it will be strong against Ice and either neutral or weak against Poison (and it is not Fighting). Currently, this only really fits Rock-type (as long as we only consider types that aren’t eeveelutions yet), or a new type. Fairies aren’t that well connected to Ice, on the other hand, you can use Light in two senses, where it would make sense for both the known strength and weakness. Whatever type it is, it should make sense with what we know, and have seen about Sylveon. I’m fine with a new type, it’s the name that I get a little irked with. ^^;