and the dog is afraid of a bird...
And we have a bird that is super-effective against a dog!
Well, more of what I'm noticing is that there may be a starter pattern here, similar to last gen. Last gen we had palladin/mage/ninja, wheras this gen it seems to be continuing having the three as a connected trio in the form of Dog/Cat/Bird, three animals commonly associated with each other. Again, another bit of a stretch, but just interesting to note.
Now one thing I have to mention, because it's got to come up sooner or later, is the question (and I'm sorry if this has been brought up already): will there be a new type introduced?
I remember when X and Y came up everyone thought there would be a new type from the start (with sound and light as common guesses), and the discussion on it was shut down because "there was too much of it" and "it was highly unlikely". Well, we did end up getting a new type, so that was kind of bad reasoning, but I do remember it getting out of hand last time. It was all speculation and almost nothing based in what we knew (at least until Sylveon was announced), which is why it had been shot down.
That being said, I think the topic should at least be broached, as we don't know the legendary typing and there is now precedent, what with X and Y introducing fairy type.
For me, I would guess no, even with not having clear legendary types. It's too soon after X and Y adding fairy to mess with the metagame again. They need time to flesh out the fairy type, so I doubt it's something they'll do.
However, playing the opposite end of the spectrum, I could see a potential "space" or "cosmic" type, applied to both legendaries, based on the oddly tech/space look of their eyes/visors/whatever those are. It would fit with sun and moon and would fit pokemon that exist as well. However, again, I think this is highly unlikely. I just wanted to put the topic out there so we could have it and be done with it. We don't know the legendaries' typings yet, so it is possible that they're hiding it for that reason as with Xerneas, but I think that's highly unlikely.