Every new Coro Coro lists the Pokemon's Type as "Unknown" or Secret. It has ? ? ? in the place just as Yveltal and Xerneas do. They did the same thing with Reshiram and Zekrom when they were released. The only reason they do that is to not tell us what the type is. Its just marketing strategy to make us (well Japan) go watch the movie since Ninfia is going to be the center for the mini episode before the Genesect movie.
Also keep in mind that Meowthe somehow causes the Evolution in the movie. So its most likely an evolution based on Item that Meowth brings to/drops on Eevee.
As for it being a new unheard of type, very low chance right now. Its most likely Normal given its very plain appearance. Hope its Dragon though.