A headcanon I've had since I was 15. Still haven't abandoned it because it's silly and makes the entirety of the Slowpoke line that much more awesome. Be sure to share your dumb headcanons in the comments.
From DineshThePoet, "The color theme is highly intriguing. Or is it just a gimmick? One of the rumors did state that Xerneas would be found by the Stonehedges and Yveltal will be found atop the mountain. Hmm.."
The theory is taken from Pokebeach. I merely made the meme. I think this is a very legitimate theory, solid all the way through.
The six most ubiquitous theories regarding the new Pokémon.
This also goes hand-in-hand with the Nordic "Tree Of Life" rumor related to Yveltal and Xerneas. Maybe all Mega Pokémon are based on Nordic Gods and that is why there are a limited number of them.