There's still role based access control and similar models that you can apply. As well as trusted path execution for binaries. While none of this is bullet pro

There's still role based access control and similar models that you can apply. As well as trusted path execution for binaries. While none of this is bullet proof, it does add a very customizable kernel-level "sandbox". If you can't run your exploit for example, even thus the kernel is vulnerable, well, too bad. Now for dreaming out loud, let's go code an OS in Rust that mimics most of Singularity and adds some RBAC on top for good measure (even thus its a much lighter version than on traditional OSes due to the system call avoidance and inherent sandboxing of all apps, as well as the contracted messages.)