>>12364150The following is confirmed:
a) It doesn't share a type with any previous eeveelution, including eevee itself.
b) It's not fighting type
c) It's super effective vs. ice
e) it's weak versus poison
d) it's not steel type
Given that the only type currently weak to poison is Grass and Sylveon is explicitly not grass type, the type chart has changed at the very least.
Given that all eeveelution names reference their type, and Sylveon's names all reference fairies, and it's got a mysterious poison-weak typing, it is presumably fairy type. Or some other type for which "sylph" is an appropriate reference.
