Well so far it's probably safe to say that Ash will get a Rowlet, as for other pokemon Ash might get early on judjing from the previews it seems like some pokemon that he might actually catch are Litten, Grubbin, and Rockruff, but there is also a chance that he may not get them. Also in regards to it being pretty much confirmed that Litten will go to Ash, I have to disagree, as while it's certainly possible that Ash could get one, it's not necessarily true that Litten couldn't go to someone else instead for instance one possibility of who it could go to would be Kiawe as if you look in this poster:
http://www.serebii.net/corocoro11164.jpg you can see that it's actually location wise is much closer to Kiawe then Ash it's all the way in the back where as Rowlet is more closer to Ash being closer to the front.
Plus for all we know it may be awhile before Litten actually joins the main cast as if you look at some of the other staters in their respective episodes you can see it took Chespin 10 episodes, Chimchar 51 or 52 episodes, and Mudkip 17 or 20+ episodes before they joined the main cast so it wouldn't be that much of a stretch really to think that it may take a while before Litten joins the main cast. As for the arugment that some of the other main characters can't get Litten because they already have a pokemon with them that seems to be their main which means they can't get Litten, that wouldn't really stop them from getting Litten as Brock having Forretress and Clemont having Bunnelby didn't stop them from getting Mudkip, and Chespin respectively.
Again I'm not saying that there isn't a chance that Ash could catch a Litten and it could join the main cast early, there is a chance that could happen, but don't be so surprised if either someonelse winds up being the one catch Litten or if it actually takes awhile for Litten to join the main cast.