It's a universal truth that there will never be a reasonable number of Pokemon in the world. We've passed the 720 mark, Nintendo will inevitably release more games, and it's likely we'll pass the 1,000 mark by at least 2020. Especially since a new Pokemon is apparently debuting in the next movie.
Coro Coro magazine has screenshots from a third Pokemon XY movie. It isn't coming to Japan until 2016, but as you can see from the images above, it suggests a new legendary Pokemon is poised to appear. When in the shadows, it resembles one of the legendary golems from Pokemon Ruby/Sapphire, but has something of a bird-like appearance when better lit.
We won't know the identity of this mysterious figure for some time. The third Pokemon XY movie will be released in 2016. Though, if a new installment is announced between then and now, we could learn what it is much sooner.
Image credit: Serebii