Some random mix thoughts.
I wonder if there are any music mixes that used objects beyond the height speakers? The system forces you to define 7.1 bed vs objects. So you make the height speakers objects and pan them to the hard default spots. Your mix comes out as expected. So the only element that will scale to different speaker arrays in most music mixes will be the height channels alone. The 7.1 bed is static.
Film vs music does have different goals. Not to add to the film vs audio divide or attribute write or wrong to anything. Film needs dialog to come across, dialog to come across, dialog to come across, and then cinematic folly fx to be on point. Natural and not gimmicky sounding and in the right spots on the sound stage. (This can require some advanced mixing chops that some audio only guys don't have, mind you!)
Music wants to make the instruments and sound elements as clear as possible. As full fidelity as possible. Usually hyper-realistic. And with the ability to be delivered by sometimes below average sound systems. For an example of that thinking, a kick drum is not placed 4" to the right to precisely image it how it was placed in the recording room. It's mixed in mono to both front speakers to couple those speakers together and make it easiest for any system to make a kick drum sound.
There are old school moves all over mixes and then maybe a few cinematic effects that can get away with only being heard in full on a full system. Any cinematic mix element could use the object system to advantage. It just doesn't apply for the old school mix elements. And of course that's what the bed tracks are for.
At the end of the day, a 7.1.4 mix can be delivered 1:1 to a consumer's 7.1.4 speaker system. Or it can be downmixed to stereo by the Atmos binaural system to sound like an actual proper accomplished stereo mix that used binaural elements.
I imagine someone will try to make a surround mix while only listening in binaural in headphones with the Atmos system. Then play the game of "What does the mix sound like on different large speaker arrays?" That seems like it would be a more niche weird thing to do. Like something the Flaming Lips might do. I suspect most people are going to continue to mix on their preferred speaker systems. 7.1.4 has landed as a reference point for that.