This is approaching the idea of Qubes OS, which is a good direction IMO and something I've been waiting for stability to try.
NixOS doesn’t sandbox apps by default (obviously, the user could run all their apps using containers/VMs/etc, but the same is possible on other distorts).
I think qubes or something like it will be the right way to go for safety in "the future" - but Inwoukd like a really simple way to define my qubes upfront- really really simple.
maybe they have it - not looked deep enough