I have an idea for another crossover...

Laughing Coffin: Apocalypse Equestria
After spending three years in the human world, Sword Art Online survivor Sunset Shimmer returns to Equestria with Luna Katsuragi and Pinkie Pie in tow. Only to discover the world has been Ravaged/Devastated by Tirek. Can an exile, black swordsman, and gypsy bard fresh from the lunatic asylum (not to mention former human sociopaths) defeat a semi-phenomenal nearly cosmic being and Discord in a world where Princess Cadence and Nightmare Moon failed so epically? Featuring Yui as Luna's imaginary friend/daughter.

Sunset would have been put in the asylum for claiming to essentially be a 'pony princess from a parallel world' during the questioning/interrogation after surviving the death game.

Luna, a beta tester or game designer (for obvious reasons) would have been thrown in the asylum while trying to rescue Celestia in the ALO arc.

And, Pinkie Pie would be thrown in the asylum during the Gun Gale Online incident... because she and Maude conspired together (or worked in concert) to kill players/competitors during the bullets for blood tournament.

All three would naturally have to organize a break out and all would have a tragic backstory.

Sunset would have joined the Moonlit Black Cats, consisting of Fluttershy, Rainbow Dash, Gilda, and AppleJack who was recovering from the loss of Big Mac, while clearing the first floor. Sunset would later meet Apple Bloom during the dragon-tamer filler episode but would fail to report the death of her siblings. And would later join Laughing Coffin because she bought into their philosophy of justifiable homicide.

Pinkie Pie would have been hit with a bale'foal' polymorph spell early on in in the game and would spent the first third of the game as a pony (and if I wanted to go really dark be used as breeding stock for a racehorse mini-game). Upon being rescued by Starlight Glimmer the two found'd Laughing Coffin. A group of player killers or grief'ers who justify blood vengeance, death, and destruction as a way of ending the suffering of others.

Luna would more or less be Kirito save a few cosmetic details and Celestia would be the deputy director of the Knights of Blood instead of Asuna. The romance would be replaced with a more platonic relationship and the plug would be pulled on Celestia, who never recovered from the ALO Coma, while she was simultaneously forced to marry Discord posthumously. Discord has Luna declared clinically insane and gets to keep the Company that owns ALO.

These backstories would be explored interstitially as the story would take place mostly in Equestria. Wherein what remains of Laughing Coffin and the mercenary Luna discover not only is Celestia is still alive, but that they must team up with a group of incompetent rebels. Rebels that bite into their feels with a vengeance because the team knew their alternate reality counterparts died because they were just as stupid. . . except for Twilight Sparkle who was more or less rendered into vegetable.