According to the official site, Mega Altaria's primary stat boosts are attack and special attack, with a physical defense boost also being brought up. Man, what a waste. Altaria's so bad right now it really didn't need to split those extra points in both attack stats. Sure, you won't know whether it's physical or special (probably physical, with the presence of Outrage and Pixilate Return), but off something like 100 attack without a held item slot? It would've been a heck of a lot better had they just said screw special attack, let's jam all these points into attack instead. Or better yet, since it's a defensive Pokémon, they should've given it just enough points in attack to make Return powerful enough, and added the rest into both defenses (preferably special, because Cotton Guard).
Mega Lopunny looks a lot more promising though, with a massive attack boost combined with further added speed. Now THIS is what it really needed.