Wow, just saw the news, looked briefly at the comments and gonna try and sum up my thoughts. Apologize for the long post:
Looks like the Bewear leak ("real leaks" leak) got another Alolan form correct (rattata) but messed up slightly on the typing (normal/dark instead of pure dark). It seems they either have partial information or early information, etc. All the more reason to be mindful of it, but skeptical.
As far as Megas.. hasn't it already been confirmed in an interview that they ARE returning, just that they aren't confirming any new forms? Not saying people can't be disappointed if there aren't any new forms, only that we don't have to worry that the ones we do have will disappear all together.
As for z-moves, I'm seeing a lot of mixed comments on the matter (not exclusive to this forum) of people saying that they are either useless or OP. Now, we can certainly have our own opinions on the features and that's fine, not saying we have to like them or dislike them or agree with me, etc, but here are my thoughts on the matter. I think z-moves are a way of contending with Megas and giving every Pokémon a chance to do something "great" or "useful" or what have you to appear in the meta game. They are only one use, but Megas are also exclusive to one Pokémon. At best, z-moves looks like they will be able to sort of OHKO a problem Pokémon on the other team if used correctly... So say someone is dominating with Mega Gengar or Kangaskhan and you don't have anything to deal with it on your team. You pull off your z-move, either severely crippling it or fainting it, and level the playing field once more. I think it's a smart feature in an attempt to add balance in the game, and can only help with Megas and not hurt. Plus, it's only one use, and your opponent has one too. Even better is it can become a game of "who has the z-move?" If you use it.
Only time can tell if z-moves are useful. To me, I think they will help and can be beneficial to the meta game, but I don't think I'm likely to use them in my play through of the campaign. As for some Pokémon getting their own Z-moves, I think that's just part of how marketing goes. I can see why some people would prefer a mega Snorlax over his own z-move, but it's not what they decided to do, and I'm not really surprised they highlighted the z-move feature in this way with a few exclusive ones. I don't think it was ever a question of "z-move OR mega" when it came to the designs, but rather "how are some fun ways we can expand on this z-move feature in our lore with the kids?" Thus we get "awake" Snorlax, as a play on the ongoing saga of his sleepiness.(on a side note, looks like his regular sprite model has been changed to lying down again XD. After all that progress you made up to X/Y Snorlax!)
On another note, it doesn't seem that exclusive z-moves (like snorlaxium Z) actually cause them to change form, only get their own z-move and animation for said move. Even Alolan Raichu we know already has that form before performing his z-move, and actually seems to get it because of his form (the surfer motif). So the info in the Chinese leak that says some z-moves unlock forms looks more and more suspicious. Doesn't prove the Chinese leak wrong (already predicted a lot of Pokémon right) just goes to show that every credible leak thus far has suspicious information, and that we must always be at least a little skeptical.
