I would imagine that the primary reason cut scene quality assets aren't used in normal gameplay is because they're too expensive to render, not because of IO limitations. It's usually things like the player character, NPC's and lighting which get improved for cutscenes.
It's not the quality that matters in this respect, it's how large the assets are. Unless you can have instant access to over a third of your game content within seconds at any given point in the game then there's no reason why 36GB of RAM shouldn't be sufficient to pre-cache anything that's needed (assuming an average game size of 100GB) outside of fast travel. The assets that you need immediate access to can be insane quality and still fit into 36GB worth of RAM. Consider that the entirety of Horizon Zero Dawn is about 40GB, and that's the whole game, not just what's available to you in the next say 10-20 seconds. If your immediate environment in the game is taking up more than a third of your total game content because the assets are such high quality, then there isn't going to be much variety in the game is there!
The discussion was spawned from the question of what PC you would have to buy today to match or exceed next gen console performance, so the percentage of PC's on the market now which meet that criteria is a separate topic. Naturally most won't and the vast majority of PC's on the Steam Hardware Survey won't be playing next gen games without an upgrade anyway so it's a bit of a moot point. But next gen games certainly can state minimum RAM requirements if they deem it necessary to be able to deliver the same experience on PC as is provided on consoles, and it certainly wouldn't be unreasonable for those requirements to be much higher than they are for current gen games. Anyone not meeting those requirements would simply have to reduce their memory requirements by doing things like reducing texture resolution and draw distance - or suffer pop in and poor performance.
I totally agree. And for PC's that do have super fast IO then delivering an experience like that available on the consoles may be possible with much lower amounts of RAM. But more RAM is an alternative that's likely to meet most game requirements, and for the majority of people will be cheaper.
Also don't forget that DRAM is much lower latency and higher bandwidth than even the PS5's SSD so there are benefits to be had from pre-caching in DRAM over more direct reliance on the SSD too. Ideally a high end system next gen will have both options.
