Earlier today, Dynamite Entertainment sent out a press release about an upcoming comic called Prophecy, featuring a host of characters from different genres and IP owners. Vampirella, Red Sonja, Kulan Gath, Dracula, Eva, Herbert West The Reanimator, Alan Quatermain, Athena, Dorian Gray, Purgatory and Pantha were among those named. The problem, though, is that it won't work. Not that I doubt Ron Marz or his ability as a writer, but there's too many pieces that inherently don't work together.
But the story doesn't really work at a more conceptual level. The world which is inhabited by Superman, Batman and Wonder Woman is a different world than the one inhabited by Noora, Jabbar and Hadya. They're both based off the real Earth, of course, but take off in slightly different directions. Super powers exist in both worlds, but people react to them very differently. In JLA/the 99, the heroes are all dropped into the same world with no explanation, but it's the DC world they're in and the 99 feel out of place. The unwritten "rules" that govern the powers and actions of the League aren't the same as those that govern the 99.
Alan Moore took a different approach with The League of Extraordinary Gentlemen by entirely redefining all of the characters. The Allan Quatermain in LoEG is a very different one from King Solomon's Mines. The same holds true for Mina Harker, Captain Nemo, Henry Jekyll, etc. None of them bear anything but the faintest resemblance to their originals. Although ostensibly a pulp novel cross-over of sorts, Moore really created more new and original characters here than in Watchmen.
It's not impossible to make a cross-over work, as the last two examples I pulled out demonstrate. But simply dropping the characters into the same space won't work. Either the characters themselves need to be changed to better mesh with one another's worlds, or the world the characters inhabit has to be markedly different than their original homes.
Granted, it can be kind of fun/amusing to imagine Captain Kirk trying to phaser his way past Darth Vader. But if you try to start building a story around that, it falls apart quickly. How does the Federation exist alongside the Empire? Even if you assume they're just from star systems that are very far apart, can you imagine the Federation not getting immediately infiltrated by Palpatine's henchmen? Wouldn't the replicator technology effectively eradicate the poverty on Tatooine almost overnight? This is the type of stuff I'm talking about when I say the worlds don't work together.
And Dynamite wants to put Vampirella, Red Sonja, Athena and Dorian Gray in the same book? You can say I've got a limited imagination, but I can't see a way that works well, even given the limited information we have on it so far. Marz may well have fun working on it, and there will probably be some good individual scenes, but a whole story? Don't think so.