I mentioned when I was talking about Avengers: Earth's Mightiest Heroes, that I prefer stories where villains fight each other with the heroes caught in the middle, to the more recent trend of heroes fighting each other, while the villains make hay off the circumstances. Which reminded me of an idea I'd had years ago, that I only ever really laid out in the comments of a comics review post back in 2009. It wound up being irrelevant, because I was operating off one idea of what was going on in War of Kings, and the truth wound up being different, but whatever.
The Magus was in charge of the Universal Church of Truth and its billions of fanatical adherents, whose faith energies were ramping up his powers considerably. Star-Lord was supposed to have stopped that with the Cosmic Cube he got from Kang, but Magus outsmarted him and then kept himself in the shadows for awhile. So figure Kang shows up, either with his usual forces, or the army of Starhawks he'd compiled from across the multiverse (as the Magus' ascension was somehow going to spread to dominate all timelines), ready for war against the Magus. Maybe Kang stops to kick Star-Lord's butt for being useless and reclaim the Cube, or maybe not.
One of the end results of War of Kings was the Fault, the result of the explosion from the Inhumans' Terrigen Bomb tearing a huge hole in space, leading to a place where anything was possible. Nova and Darkhawk eventually encountered not just one Sphinx, but two, one young and one old. The old one was struggling to correct past mistakes, the young one didn't see himself as making any mistakes. And each of them had an immensely powerful Ka Stone, and if either got both, well, that would be a serious problem. So have one of the two emerge from the Fault more powerful than ever, with the Sphinx' usual plan to become a living god over all humanity. Clearly not something either of the other two would-be despots is going to tolerate.
In the middle of that, the Guardians of the Galaxy, Nova, Darkhawk, Namorita (who was brought from an earlier point in her life by the Sphinx, and then Nova kept her from vanishing when the whole place fell apart). Commenter Sean Greyson had mentioned wanting to see a Guardians of the Galaxy/Young Avengers team-up, so throw them in there. This story involves Kang, which is who Iron Lad became (and who that version of the Vision's brain patterns were based on, if we want to use him instead), so there's a reasonable justification.
I also wanted to throw in the outlaw Avengers team Justice was leading back on Earth - this was concurrent with Dark Reign, when Osborn handed over control of the Initiative school to the Hood. One wonders how that got through Congressional appointment hearings - because that would have been about as close to a New Warriors reunion as we were likely to get. Besides, even with that many heroes, they're still seriously outgunned, both in raw power and sheer numbers. Hell, find some justification for the Agents of Atlas to get involved (have Namora find out her daughter is alive and she'll charge out into space in a second).
Then factor in the Inhumans, reeling from the loss of Black Bolt, dealing with some hostility from the rest of the universe, since it was their bomb that caused the Fault, the Shi'ar having lost Emperor Vulcan and Lilandra, now a pale shadow of their old selves. Blastaar is out there as a king, looking to establish himself, get whatever he can, and settle some grudges (both Nova and Star-Lord had pissed him off recently). The sheer number of players, conflicts, uneasy alliances, the scale of the battle which could be taking place on different worlds across the universe, I would have been willing to spend so much money on something like that.