Ash is most likely going to lose.

I can't recall Ash having done a single dumb thing during the entirety of XY so he wont lose in that way, and we already know his opponent in the final round is not another Tobias situation but instead Alain who's an established character that Ash has battled already. 

http://satoshipediaeng.altervista.org/ashs-age-in-each-series/

It'd be funny if his trainer gets another Uber legendary and destroys ash.

I'd love to see Mega Rayquaza destroy him

So a fan theory on how old Ash should be, keyword being should, not actually is. Real canonical proof would be episode 1 of the BW series where they blatantly say he's 10 years old still, thus the show clearly does not use real world time logic.

Part of me hopes so, just so that it could lead to something interesting with the anime going forward (and maybe a huge SerenaXAsh moment. Yeah, I ship it!)
But I think they'll make him lose in the dumbest way possible, bonus points if its the Final Match.

Whoops.

You can ignore my previous post then

being in the Kalos League finals is the closest Ash has ever been to a League Championship outside of the Orange Islands. XY/XYZ has redefined what the series can be by going away from the usual formula while providing more crisp animation, especially for the battles. Would it surprise me if he won? From what I've seen throughout this series, no. Though I wouldn't be mad if he lost to Alain due to the fact that Alain's character has already been developed from the Mega Evolution series that was running alongside the main series and, those who know the character, has shown what he's made of. Can't wait to see what happens.

Well, I just took one quick glance at the Wikipedia page for the remaining XYZ episodes.
Go to the link at the risk of spoilers.
You have been warned!
https://en.wikipedia.org/wiki/List_of_Pok%C3%A9mon:_XY_%26_Z_episodes

Son of a Bitch there's really been over 900 episodes of the anime?!?
J-Jesus!