Got in late for the HOS discussion, but I don't think we're going to see them use the exact same HOS used by Switch. More like HOS 2.0, where the baseline for it involves its security. Even though Switch got hacked early on, it was because of the convenience of the entry point being well documented and public from the situation with the Shield TV. Hackers had said that if it wasn't for that point of entry, they would still be looking for another opening, perhaps even now, because they felt that HOS was that secure.
The way HOS works with memory is it partitions it into 4 sections - Application, Applet, System and System Unsafe. The latter two are, imo, the basic portions of the OS, which together allocate roughly 310MB. Application is for the games, taking ~3.2GB. The remaining 467MB is for Applet, which is everything else, like the Home Menu, Album, eShop, Settings, even the All Software list etc, and as you move into each part of the system, the prior stuff is emptied out and newer stuff is loaded in. Areas like the eShop and Album are loading in data as you scroll through them, but aren't retained because there's only a limited amount of memory to work with, so when you scroll back and forth, it's continually reloading. For the eShop, the data isn't located locally, so it has to continually download. While folks suggest that the reason Nintendo didn't include a fully loaded internet browser was to avoid a hacking situation, it could also be because of the limited amount of RAM that would have been available to it. Can't really compare it to the Wii U, because as time goes on, there's expectations from things like that, like using the latest software, and the available RAM likely couldn't cut it.
For the eShop, the CPU is used heavily, using the 3 game cores when a game isn't loaded, but is limited to the OS core when a game is loaded (the latter of these two scenarios brings the eShop to a crawl). Back to the point of the eShop redownloading data as you scroll, this is likely why the eShop uses a good amount of CPU. I think it's having to process this data, which may include decompression. Let's say it is having to decompress data for the eShop. With Switch 2, if they redesign the eShop, they could possibly make use of the FDE so the CPU isn't being pushed, which could make browsing the eShop much faster (besides having the stronger CPU).
What I'm getting at ultimately, is let's not think of Switch 2 using Switch's HOS "as-is", but as a baseline for the important things while also being expandable in content, features, and functionality.