It's getting to the point where the writers might not have a choice in the matter.
I mean we've got another thread with discussion of how in the heck he's supposed to get past Korrina's MegaLucario and she's only the third gym leader. If things are like this now, what exactly does the future hold, cause I for one don't see anything good.
Now I know the rest of the GL's might not use legendaries, but i'm more worried about Team Flare and the League, when Ash gets to those points and is faced down with Mega's, I question what the writers will do.
Oh sure Ash could maybe beat a mega if someone uses one in the league, but if takes half or most of his team with it, he still loses and it continues to show just how strong mega's are from how many of his pokemon it took to take one down.
As much as I want Ash with a Greninja, until Mega's first showed up in the anime that would've been my top wish, but now I want Ash to get a Mega before anything else, because unlike catching a legendary pokemon, something Ash can never do, getting a mega to counter opposing Mega's is something he can do, and it would be stupid to not take advantage of it.
I agree though that using Mega's constantly is overkill, but against Team Flare (possibly Alain) and the league he should have one, I don't care who it is, or possibly both Sceptile and Charizard.
Heck to be honest I kinda want him to learn the process before battling Korrina, and even if his pokemon has abit of trouble, show Korrina and everyone else how strong his bonds are with his pokemon.