Because of Askia’s story in the DC-Marvel-merger thread, mostly.
Here’s your setup:
The Big Three (Superman, Batman, and Wonder Woman) wake up one morning lying on the front lawn of Xavier’s School for Gifted Youngsters, badly wounded, completely dazed, and unable to remember a single thing. Prof. X senses them with his telepathy and sends a small team of heroes (Wolverine among them) to check this out. In their confused, delirious state, the Big Three think they’re being approached by enemies and prepare for attack.
Meanwhile, back in DCU, the rest of the JLA are frantic. Their major superheroes have mysteriously gone missing and an apocalyptic crisis (of your choosing) is facing the world. They need to get Superman, Bats, and Wonder Woman back at all costs.
Ready? Go for it!
You need to have parity. If three top heroes have disappeared from one world you need to balance it with a counter-disappearance. So at the same instant that Batman, Superman, and Wonder Woman appear in Salem Center, Captain America, the Hulk, and Spiderman appear in downtwon Metropolis. The Avengers, like the Justice League, is investigating the disappearance of three well known heroes. Whoever the entity is that’s responsible, the three unknown people who appeared at the same moment are probably its agents.
And the first person to contact Captain America, the Hulk, and Spiderman is Lex Luthor. He offers them shelter and information; both carefully crafted to make the heroes think that he’s a good guy whose trying to free humanity from the tyranny of the so-called Justice League.
Okay, since we haven’t started writing this yet – note only plot points have been put forth, I’d like to make a few suggestions and ground rules that are, clearly, up for further discussion:
First of all, I’m not sure the Marvel equivilents are listed correctly. I would think the closest analogies are Captain America, Iron Man, and Scarlet Witch (The closest thing I think Marvel has to Wonder Woman is Ms. Marvel, but I’ve lost track of her. She-hulk could be a possibility, and I would be willing to swap Thor for Iron Man.
Luthor is a great idea, if you’re going for Mirrors, the DC trio would be found by Doom, But I like the idea of involving the X-men as it gives us a chance to involve the Titans from DC.
So, what I’m proposing is that instead of a traditional finish the story we actually work at collectively crafting the story bit by bit. First lay down the plot, then actually go about writing it in installments.
Not what everyone was expecting, but it would easily be fun.
Actually, we don’t need to have parity. It’s Kytherias thread so it’s Kytherias rules.
Next up, if there is going to be a switch to maintain parity, the trio should be Captain America (Icon), Spider Man (Icon/brains despite what Tony Stark will tell you 
), and Spider Woman (token chick).
If it’s going to be an X-Men switch, you’d have to go with Cyclops, Wolverine, and Storm or Rogue.
Also, Doom would be a lousy choice to discover the heroes from DC because he lives in his own lil country(Latveria) set aside from most of the Marvel Universe whereas Luthor lives in Metropolis. He’s also much much much less subtle than Luthor is.