I still say that Fennekin's line will remain pure Fire. There's only been a single pure Fire starter line, while both Grass and Water have had as many pure lines as Fire has had Fighting subtypes. Honestly I feel a Psychic subtype is one of the least possible subtypes for it, even without the thought that it could have been using Copycat or something like it.
I'm going to agree with this statement. Most starter's can learn multiple type of moves they are not within the first couple of stages (hence, Grotle's Bite/Crunch, Totodile learning bite, exc...) and therefore could just be a pure fire. the legend fennekin is based off of is basically just a firefox in the end (not Mozilla) and will probably be a Pure fire type.