Fennekin is without a doubt going to be a psychic type eventually based on its name and it using Psywave in the trailer. Deciding what it's stats are going to be is based on logic and previous patterns combined with what would they should be, because I really see Fennekin being in OU when it is fully evolved or maybe even Uber like Blaziken.
Hp 75 Attack 65 Defense 70 Sp. Attack 120 Sp. Defense 80 Speed 120 Total 530
Chespin is probably going to be a dark type when it evolves, because it looks a lot like Seedot (brown with grassy parts on it). Deciding what it's stats are going to be is based on previous patterns of pokemon that evolve into dark types and the pattern of physical grass type attackers. I predict that Chespin be in OU when it fully evolves to make up for the previously horrible grass types in generations 4 and 5. It seems like it would be an offensive pokemon similar to Fennekin, but more versatile and unpredictable.
To answer your questions, Game Freak said they wanted to make a game EVERYONE wants to have and give major improvements so of course the starters must be good. It is not what I want that WILL happen, but face it, Fennekin is a pokemon that was made for people to like and even favor as a starter since Game Freak test runs first how people will like the designs, so it would more than likely have stats that go with that.
Also, Lucario CAN'T learn Psychic without TMS!!! Psywave is NOT a TM, so that IMPLIES that Fennekin will be part Psychic type since it learns that naturally. Yes Misdreavus and Mismagius can learn Psywave without a TM, so there is a small chance that it could be Ghost/Fire but what are the odds of a ghost type starter?