The problem with this is opportunity cost. You give up your mega slot (and ability to use megamence or megaray) for something that frankly doesn't do much else besides counter Zek. And with Megagroudon, zekrom is gonna face a lot of competition for a slot. Even then, better options exist. You can always run a fairy+ground to counter it anyways, and you also get the ability to check other things. On top of that, steelix is dreadfully slow. It's just gonna be a subpar pokemon with no niche.i can see mega steelix having a niche in uber battles for being a hard counter to zekrom since it isnt even 4HKO'd by a choice band outrage and it is immune to bolt strike/volt switch.
steelix can 2HKO with EQ due to its buffed attack stat.
To add to what Alert to Sounds already noted, Fairies will also be a hindrance to Sableye, and the opportunity cost of using up a mega slot for something that's kinda mesh isn't that great.Not sure if Mega-Sabaleye has been brought up yet. 50hp is going to hold it back but got good defense and only 1 weakness finally a bulky magic bouncer. One of the new mega I want to try in uber in ORAS. I predict it to be popular in uber, lets just see.
A cool niche it does have is that it is a perfect Stalltwo counter for all Mewtwo formes, boasting immunity to Psychic and Fighting while Magic Bounce reflects Taunt and Will-O-Wisp. I don't think that's enough of a reason to use the Mega though.
Diancie @ Diancite
Naive Nature
4 Def / 252 SAtk / 252 Spe
-Moonblast
-Earth Power
-Diamond Storm
-Stealth Rock / Heal Bell / Calm Mind
Moonblast and Diamond Storm are obvious STABs. Earth Power 2HKOes Primal Groudon and takes care of most other Fairy resists. The 4th moveslot is utility: Calm Mind can potentially enable a sweep, Stealth Rock is cool on a Magic Bouncer (you can set up SR against a lead like support Dialga or Deoxys-S while they can't set up theirs, giving you momentum, free Rocks, and a free Mega Evo), and Heal Bell lets you act as an offensive cleric which is useful on a lot of teams.
This has a lot of notable advantages over Xerneas: the deer would certainly kill to get Earth Power or Diamond Storm (which makes Ho-Oh a non issue), its faster (outspeeding Palkia is sweet), and SR gives it utility Xerneas can't provide. Very dangerous Pokemon overall, even if you're busy drooling over Ray/Mence don't underestimate this princess.
Okay, so i'm just going to do a bit of theorymonning here, but I think that xern will actually be BETTER in ORAS. Why? because Primal Groudon beats every common geoxern check possible. Aegis? nope. Lugia? uh-uh. Ho-oh? nope. megascizor? Heck no. even other primal Dons lose to a suprise special set. However, xern will want to run HP ground from now on. It still hits the common switchins and most importantly beats Primal Don.
Okay, so i'm just going to do a bit of theorymonning here, but I think that xern will actually be BETTER in ORAS. Why? because Primal Groudon beats every common geoxern check possible. Aegis? nope. Lugia? uh-uh. Ho-oh? nope. megascizor? Heck no. even other primal Dons lose to a suprise special set. However, xern will want to run HP ground from now on. It still hits the common switchins and most importantly beats Primal Don.
I don't think Xerneas can any get better than it already is right now, even though I don't deny that Primal Groudon could help Geomancy Xerneas out, there's something that could be considered uncompetitve that it's buffering it,Shadow Tag mons, those can help beat all of the checks and counters you mentioned in your post, I'm not going to mention them because that would be getting off topic. If you really want to know there's a Shadow Tag suspect test that I highly suggest you to look at :]Okay, so i'm just going to do a bit of theorymonning here, but I think that xern will actually be BETTER in ORAS. Why? because Primal Groudon beats every common geoxern check possible. Aegis? nope. Lugia? uh-uh. Ho-oh? nope. megascizor? Heck no. even other primal Dons lose to a suprise special set. However, xern will want to run HP ground from now on. It still hits the common switchins and most importantly beats Primal Don.
In my mind Ditto is something that thrives in a meta that is unstable due to a flood of offensive threats, as it's something that can be pretty much mindlessly slapped on a team and then you don't have to worry about revenging offensive threats. That'll be the case initially, but eventually the meta will settle and people will learn to adapt to the new threats and so after an initial spike in usage it'll probably settle back down again I imagine. I could be wrong tho (this is pure theory), especially since all 3 will likely be known for their offensive sets more so than defensive ones (to say the least).With Mega Rayquaza, Mega Salamence and Primal Groudon around, I think Ditto is going to be something in this new meta.
Moreover Ditto requires no team support and can easily be added to any offensive team.
So a reliable SR setter + 4 offensive mons + Ditto might work very well.
Calling bullshit on this. We'll see in a few weeks, tho.Oh Kyogre, former King of ubers, how the mighty have fallen :(