I'm not dismissing 4k as completely useless, but I'm highly skeptical that it will catch on. We'll see. However, $100k audio systems is another place where A) it's ridiculous to spend that much no matter how rich you are, and B) humans can't tell the difference beyond a certain point, which is at least an order of magnitude less than a $100k audio system. And the only reason that the price ever crept into the 5-digit range is stuff like 11.4 surround where the extra speakers and amps add up for an immersive experience, the price ceiling of absurdity is a lot less on the stereo side.
Yeah, you hit the nail on the head. I wouldn't say physical media has gone the way of vinyl quite yet, but it's rapidly going there.
I spent plenty of time yesterday listening to $100,000+ systems. You can hear a difference, period. The law of diminishing returns may be in effect, but there's a real difference between $20,000 speaker cables, and speakers that cost $20,000 each.
Esoteric cables are worthless, but the speakers at that price level sound better, in fact much better than cheaper speakers - even when "cheaper" still means over $1000/pair. Today I'm at a GTG listening to great DIY speaker pairs, plus some amazing ID and and commercial units. None of them cost 5-figures, and none of them matched the best systems I heard yesterday at the New York Audio Show. There's plenty of snake oil at the high-end, but there's also plenty of amazing engineering that really does made a difference.