This is, of course, a follow-up to the post I made earlier today. After thinking about it some more, I'm more and more certain whatever these things on the box art are have something to do with weather inducing, which makes sense considering their existing lore. However, they definitely don't look like mega evolutions to me - the apperance differences are very minor, à la Resolute Keldeo (though you can bet that unlike Resolution Keldeo, these will actually do something). So them even looking like alternate forms is a bit of a stretch, but since this is the bare minimum of what they are, I won't try to argue with TPC.
So here's what I'm thinking: these are alternate forms, presumably triggered by some sort of item. Possibly the Red and Blue orbs, which would get promoted from plot coupons to actual held items, and would work like the Griseous Orb does for Giratina. As alternate forms, there would be no BST change (though the stat spreads may be different), and they'd gain abilities (let's call them Drizzle Plus and Drought Plus) that'd work just like Drizzle and Drought used to. However, it does come at the cost of the held item slot, so you have to think about whether you want to keep Leftovers, your Choice item or whatever else or give those up for permanent weather. So those items would be Damp/Heat Rocks on steroids, but would only work on Kyogre and Groudon, and give them a slightly different appearance to boot.
That's what I'm hoping for, at least. Mega evolutions would be a terrible idea, for two reasons:
1. Do we really need Pokémon that have the ability to induce weather (regardless of whether it's for five turns or permanently)... and come fully loaded with a BST of 770?
2. Mega evolutions would be self-defeating in a way. Let's suppose we get a Mega Kyogre that knows Drizzle Plus. Kyogre gets sent out, vanilla Drizzle activates, you megavolve it... and Drizzle Plus doesn't do jack because it's already raining, just like how the counter isn't reset when you megavolve Tyranitar or Abomasnow. So you'd be forced to switch out, THEN back in again once rain is gone to get your permanent rain. Of course it could be a way to balance things slightly, but it's still just silly and defeats the whole point. With alternate forms you don't need to go through that, your ability takes effect right away.
Still, and I can't stress this enough, THEY DON'T NEED THIS. With Smogon's new weighting system, Kyogre jumped to third place in front of Mewtwo in the monthly stats. Imagine that: Mewtwo gets two devastating mega evolutions and tremendous unpredictability in the process, while Kyogre's rain gets cut to five turns. AND KYOGRE STILL GETS MORE USE.
Oh well, looks like the die has been cast, and we can only hope the devs listened to reason.