I feel like too many Megas have Magic Bounce as their ability. I mean, it's cool and all, but damn. It is the most common Mega Ability.
Only 3 Mega Pokemon get Magic Bounce: Absol, Sableye, & Diancie. It's tied with Tough Claws (Charizard X, Aerodactyl, & Metagross).
So far I think they've done a good job keeping the Abilities varied. The problem is that not all Abilities are created equal, there are Abilities which are just flat out better than others. And so when you're making something called a MEGA Pokemon, I can imagine it being real easy to just slap on these really good Abilities and not a more situational one.
For example, how do you feel about the following Mega Pokemon and their Abilities:
Charizard X/Aerodactyl/Metagross (increases moves that make contact's Power by 33%)
Charizard Y w/ Drought (summons sunlight)
Gengar w/ Shadow Tag (prevents opponent from switching out)
Kangaskhan w/ Parental Bond (attacks with the same move twice, though second attack has half the Power)
Gyarados/Ampharos w/ Mold Breaker (ignores the opponent's Abilities when attacking)
Blaziken w/ Speed Boost (every turn increases Speed by +1 stage)
Mawile/Medicham w/ Huge Power/Pure Power (doubles Attack)
Aggron w/ Filter (reduces damage by Super Effective moves by 25%)
Absol/Sableye/Diancie w/ Magic Bounce (reflects back Status moves)
Lucario/Beedrill w/ Adaptability (increases STAB from 1.5x to 2x)
Camerupt w/ Sheer Force (exchanges a move's secondary effect for 30% more damage)
Man, these sound awesome, these are truly powerful Abilities and one can say some even make the Pokemon. So with that in mind, let's look at these:
Mewtwo X w/ Steadfast (raises Speed by +1 stage each time it Flinches)
Mewtwo Y w/ Insomnia (prevents Sleep)
Houndoom w/ Solar Power (in sunlight increases Special Attack by 50% but loses 1/8th of its max HP)
Manectric w/ Intimidate (lower's opponent's Attack stat by 1 stage entering battle)
Gallade w/ Inner Focus (prevents Flinching)
Audino w/ Healer (30% chance of healing ally's status condition each turn)
Err, not so great. They're situational at best though most of a time a non-factor. They might as well not have an Ability. Now they're still good Pokemon, but when you have other Mega Pokemon getting Abilities which power them up even further these poor fellows kind of lose some momentum. Like say they had these Abilities instead:
Mewtwo X w/ Mold Breaker
Mewtwo Y w/ Levitate (unaffected by Ground-type moves)
Houndoom w/ Flame Body (opponent has 30% of getting Burn if they make contact)
Manetric w/ Speed Boost
Gallade w/ Moxie (increases Attack by +1 stage when it knocks out an opponent)
Audino w/ Regenerator (heals 33% of its max HP when switching out)
Now this is what you'd imagine a Mega Pokemon would be like. These Abilities are far less situational and even exemplify the good qualities of these Pokemon. However each Pokemon is their own and some can take a lesser Ability and make it great. For example No Guard is a double-edged sword but Mega Pidgeot loves it for 100% accurate Hurricanes without needing rain. Scrappy is useful though normally overlooked, but on Mega Lopunny who's both a Normal and Fighting type its a valuable Ability as combined its STABs hit everything for at least neutral damage. Blastoise, Heracross, and Sharpedo may have gotten move specific Abilities in Mega Launcher, Skill Link, and Strong Jaw but they were given the moves to properly use these Abilities to full effect.
I'm getting a bit side tracked so let me get to my point: I don't mind if several Mega Pokemon end up sharing the same powerful Abilities. They're Mega Pokemon, they're suppose to be the best that Pokemon has to offer, so I'd rather it have an Ability that furthers it then them choosing another Ability just because a few Mega Pokemon already have that Ability. But that said, if they can think up of a unique use for that Mega Pokemon with a certain Ability I'm all for it too, as long as it still makes me say that Pokemon is a Mega Pokemon.