I heard the new type is good against Ice and weak against Poison.
I can only think of Light/Pure type. Light melts ice and obviously Light/Pure would be tricked/killed by Poison. Light and Dark should be super effective on each other (yes, both ways). Also, either Light doesn't affect Fire or Fire doesn't affect Light. This would be pretty cool. Also, Grass should resist or absorb Light (plants absorbing light).
I've heard mention of immunity to dragon on the grape vine. I couldn't imagine how light/pure could relate to that. (I hope it's true because these SD/DD outrage sweepers are just pissing me off, I'm looking at you garchomp and dragonite)
We don't actually know if Sylveon is super effective versus ice or not. We know that Sylveon isn't vulnerable to it, and is effective versus it, but unlike the poison test, no caption came up saying it was super effective. As a result, it's possible that Sylveon is neutral to ice or resistant to it, rather than super effective versus it.