The problem with Unix is that the abstractions don't match today's adversarial computing environment. If seL4 can provide kernel-level process (tree) isolation, which part of Unix is inadequate for 2024?
You could certainly write a Unix abstraction layer on top of seL4, or more commonly treat seL4 as a hypervisor, but you would not be able simply use a Unix interface to interact with seL4 and get all of it’s benefits.
Capability based systems don’t magically carry their desired properties up the abstraction ladder, they have to be maintained and the designer has to be vigilant to avoid introducing ambient authority by using capability based design themselves.
Genode is an example of a layer over seL4 that follows these principles.
If it's not too late to ask, where can we read about that? I've only ever seen ACL v. capability discussed in terms of trades-off as far as I remember.