Vanilla OS is a semi-immutable atomic distro based on Ubuntu, that features the apx package manager. This awesome program gives you dedicated, isolated containers for all the major distros, and the ability to install apps from those sources that are fully integrated into your system, eg apx --apt instal for Ubuntu apps, apx --dnf install for Fedora apps, and apx --aur install for Arch apps. This works for command line and graphical applications, and it also has Flatpak with Flathub and nix out of the box, so you can install pretty much any Linux app.
I said “semi-immutable”, because there is a command to enter the root partition (sudo abroot shell), for doing things like installing drivers, but they recommend doing this as little as possible. It makes it a much better solution than Fedora Silverblue for the average user, with all this flexibility. I think it deserves a spot on the recommended Linux distro list. It is aiming to be beginner-friendly eventually, but it is still recommended to have good Linux knowledge to use it for now.
Last time I checked, VanillaOS didn’t have a way to enable disk encryption during install. Until this changes, I’m not sure it should be considered.
Other than that, however, I do agree, VanillaOS is a really interesting project and worth keeping track of for future developments. Another project that does a similar thing is blendOS.
Probably not. Something more faster than whatever their cadence is more desirable. Something based on Sid is probably desirable but that might introduce breakages for the user. Although I’ve heard elsewhere that Sid is pretty much becoming more and more stable these days.
Don’t get me wrong, I like the idea of having an immutable base and installing all user apps in sandboxed containers, but it’s not quite there yet and doesn’t yet provide the level of isolation they seem to imply in their docs.