I think the writers will again surprise us with some random plot twist like they have been doing since the beginning of BW. I don't know if they'll follow the in-game story, but I don't think they will, I think the TP storyline will be concluded before the league.
When it comes to Ash's position, well many people already mentioned the fact that Ash has been progressing each league in terms of rank, and even Brock mentioned it at the end of Ash vs Tobias, saying that it's the first time Ash entered the top 4.
As such, I don't think the writers will make him regress and stop at top 8 or even lower, I think he may have a chance to make it to the final match against some strong opponent. Top 2 is, thus, the minimum IMO. If Ash were to win the tournament, then afterwards in a filler arc, he could challenge the E4 and Alder (officially this time) in order to become champion material. This can work the same way as the Battle Frontier : Ash faces the E4 (which are spread accross Eastern Unova, and not gathered in a single building as they are in-game) and only after having defeated them all, he can challenge Alder in some symbolic place.
And since this hypothetical post-league storyline will take place in a filler arc, then we can introduce past gens Pokemon (with captures, evolutions, return of other Pokemon... You know where I'm going right?), which could kill two birds with one stone : Ash, league champion, faces the E4 AND 'promotes' Ruby/Sapphire remakes
So, yeah, this is my speculation about Ash's league position : Winner! Maybe the final match will be him against Trip, with Alder eager to see who the winner could be...