[to Kal] I think you missed my point. The issue isn't that you can sit anywhere on your couch and still get a good experience. The issue is that you have to sit on your couch for the duration of the album to get the experience. People 'round these parts may listen that way, but they're a tiny minority among music listeners.
I still don't think that you have identified a major differentiating issue. The sweet spot with stereo is only smaller. But you brought it up as a limitation on MCH's
relative popularity.
Most people put the stereo on and then go sit at the kitchen table to work on a puzzle, or wash the dishes, or clean up, or do some other activity that involves them not sitting in front of their sound system for most of the runtime of an album.
And to be honest, most people don't put on the stereo at all, because these days most people don't have one: they put on the
single bluetooth speaker for background. Or just pop in the earbuds: the
vast majority don't seem to mind them at all.
For those people, who again, are the vast majority, surround mixes add nothing.
I gather that you brought these matters up because you see them as a limit to the appeal of MCH in a way that stereo isn't limited.
But it could be argued the exact opposite way. Stereo music systems in the home were ubiquitous in the 1960s, but today they are an absolute oddity. That's a big crash and there's no coming back: it's stereo hifi that is the niche format both today and going forward.
Although individual tablet-based video consumption with earbuds is starting to take over, today the ubiquitous in-room-sound device is the TV, not the stereo. And all those Netflix movies and TV shows are in surround sound, and so are a huge amount of the other channels. Furthermore, those TVs today support all the music apps, so when people want to consume music, they are just as likely to play it from the TV (especially if it has had its audio supplemented), or that aforementioned solo bluetooth speaker. If it's the former, the audio supplementation is almost certainly going to be multichannel, even if it's just a soundbar, or less often, MCH speakers. Either way it will support immersive audio, which will offer a much better, more enveloping audio experience, even to the person wandering around the room doing other tasks. Even if they choose the bluetooth speaker, some eg Apple's HomePod have immersive Spatial Audio and support Dolby Atmos. They are definitely going to offer a more immersive impression than stereo, even to your task-oriented listener on the move.
And if TVs give way to individual tablets and earbuds, spatial audio is still offering something perceptually more immersive than stereo over earbuds. Even without earbuds, laptops and some tablets are starting to support spatial audio over their inbuilt speakers.
In practically every typical situation, MCH audio seems to have something to offer, and is starting to become ubiquitous.
cheers