Man, I keep seeing this one mashup pop up everywhere—'Sing 2' meets 'Rise of the Guardians'. You've got a cast of performers who've lost their passion or been humiliated, and now have to summon up belief in themselves and their art to literally stop the world from being consumed by darkness? The Pitch stands in for Clay Calloway's reclusive grief beautifully. Buster Moon convincing Jack Frost to find his voice and fight back by singing 'Could Have Been Me' is a mental image that won't leave me alone.
Another one that just works on a weirdly structural level is crossing with 'The Mitchells vs. The Machines'. It's another story about a scrappy, chaotic, found-family creative group going up against a homogenizing corporate tech force. Swap the robot apocalypse for Jimmy Crystal's monopoly, and you've got a perfect enemies-to-allies arc for the Mitchells helping Buster's crew sabotage the Crystal Tower show with glitchy, DIY tech. Thematically it's all about authentic human connection versus slick, soulless product.
I've even seen a few writers try a 'Mad Max: Fury Road' crossover, of all things. It's bizarre but oddly compelling—the wasteland becomes a world where music and performance are brutally suppressed, and Buster's troupe are a traveling caravan of rebel entertainers trying to reach the legendary 'Green Place', a functioning theater. The high-octane chase sequences could be swapped for escape-from-Crystal-stalkers scenes, with Ash providing a blistering guitar riff soundtrack the whole way.