http://www.gamesradar.com/pokemon-xy-why-director-masuda-himself-answers/?utm_source=fb&utm_medium=emp&utm_campaign=pokexyFB said:
Why...no rivals
To begin is answer, Masuda said, “At Game Freak, I mean, it’s probably a result of the first two games--Red and Blue, and Gold and Silver--having this kind of strong rival, but at Game Freak we really don’t focus a lot on having this aspect of this really strong rival, or this adversary. We don’t really use that expression over there.” Instead, he said, they focus on, “having someone who thinks in a different way as you, perhaps, or is kind of your opposite.”
Which in our playthrough meant friends! We were very excited by this feature, and were totally on board when Masuda spoke about friends in the game: “The game begins when you meet them for the first time, and then you set out on this adventure together. And over the course of the adventure you can really see your relationship becomes closer with these friends, and it just deepens as the adventure goes along.”