There isn't one in the intro because they want to surprise us. They're thinking "OK guys, what do the fans who watch Pokemon want MOST of all from the upcoming League?"
The answer, of course, is a generic League Rival introduced JUST before the tournament that will somehow steal the spotlight from Paul, Barry, Nando and Conway!
However they can't reveal it just yet. They want us to let our guards down. They want us to think they've changed by introducing four trainers that would eventually go on to face Ash in the League as opposed to Last Second Rival-son.
I won't rest though. I'll be waiting, and if he does appear, which he will I'll be ready to jump out and punch him in the face.