Sort of like Erlang? Which can run on POSIX.
> Perhaps instead of processes we'd use just virtual machines.
Sort of like the JVM, or Docker, or VirtualBox, or any number of VM technologies that run on POSIX?
> There are strong reasons to want safety and security guarantees around the lifetimes of those things.
Why do any of these things need to live in the kernel to give safety/security guarantees? If anything, code that runs in the kernel is more vulnerable, not less.
btw. I don't think POSIX is the be-all end-all or anything. But if I imagine something better than POSIX, its abstractions are even less opinionated than POSIX, not more.
I only care about OS POSIX support every time I have to go down to C or C++. Otherwise the OS can have whatever abstraction model it feels like.
All of those should properly be managed by a kernel, yes?