The problem about the League happening now is because the League is the climax of a story. The League is purposely situated in the end of a region for a reason.
When the League ends, Ash has no reason to staying in Unova. The only reason staying in Unova is for give closure to Iris/Cilan story. If anything a tournament (I see Ash winning, of course), nothing more.
The most important reason to believe that the League isn't happening is why in the series is happening:
1) The Season 2 has only 2 months and 8 episodes. Season 2 likely aren't going to be only 25 episodes.
2) The references of the League suspectedly apperars very rarely. You'll find very suspect that none of the summarys of the two episodes after the JC didn't mention the League. This is pretty abnormal.
3) The fact that we know what time last until the league but not where. The other time that's Ash goes to the league Ash is informed with the time where is happening the League. And the Junior Cup isn't a excuse.
4) When Ash gets the 8 badges Ash lose. Yes. Ash lose against Homika. Technically he win but with a unfair advantage. And Cynthia, the Sinnoh Champion isn't going to inform if happen that Ash can't go to the league. Seriously, cpuld you think that Ash can win aginst Trip if Ash suffers with a Gym Leaders, something that has a inferior level to the League participants? The recent lose against Trip is n't a good sign either. The exception is that battle is Pikachu, clearly his strongest pokemon.
5) But Ash wins against Dragonite. First, Dragonite is out of the control and second, Ash was using Krokorok that aren't one of the participants in that 6 vs 3.
6) This is minor, but the three months until the league isn't happening NOW. The three months until the league ends in theory in the Nursery episode. But because of breaks I absten of that.
7) Related to 4). For the first time in the Pokemon's franchise, the games promoted 10 badges but only 8 are required for enter the League. And the writers of course could wanted to promote all Gym leaders with battles with the anime representant (read: Ash). This is important because of this, why do you think that Ash is going to battle all of Stration Trio? But the only option is with a official punish from the League happened, something that can happen now than ever because now makes sense. And the possible cause is going to be 4).
8) The rivalry of Georgia and Burgundy aren't closed anymore.
9) And the most important. If the league starts in October, the league is ending in December of this year. And Ash is going to stay in Unova until September 2013 or something because training. The writers can't put Ash without a goal for more than 5-6 episodes. In resume, Ash must do something until the 6th games happened. Yes. the new games aren't releasing until end of August 2013 at the earliest. I don't thin that BW last 190 episodes or so, but I can that he can last 140-170 episodes. And the games could release in 2014, probably not in January but can be in Spring 2014, for example. And the Gen V method of showing Pokemon isn't the only method. Although i can't think convenient that Gamefreak didn't want promothing new pokemon 2 years before the release. But you remember that DP was announced in 2004 with release 2005, not September 2006.
10) Something interesting. I can't see Iris leaving unova with Ash because the roles that has in the sequels. That's Iris is Champion in the games has already having effect in the anime. Only because that Iris caught Dragonite, and that Dragonite has a Champion-level, surpassing any of Ash's Pokemon. And Ash only win against it because he was in a rampage. That's explain why Iris admires Cynthia. And why Iris challenges Cynthia in their first place. And I can think that a team of Dragonite, Haxorus, Excadrill and three more is Champion-worthy. I think that when the anime staff knew that Iris is Champion would be shocked. And I don't think that the anime put Iris in the anime if they know that could be Champion later.