I don't exactly see that as any better security. The assumption nowadays is that once something breached application safeties and has user level access to a machine it is as if it had root level access to that machine.

The reason is that there is just too much surface between an application and the operating system to be able to guarantee safety.

And so we put applications into their separate VMs or containers and treat the entire container as part of the application. There are no other assets on that container.

If the container boundary is meaningful, you can do things like run TLS termination in a container (because OpenSSL is a quagmire), and connect to the server via unix socket. Then the container has no need for outgoing network sockets, and limited filesystem access.

Of course, if the container boundary isn't meaningful, you've complicated your system design for nothing.

And either way, TLS termination in a separate process is a potentially significant penalty to performance, as you'll have a lot more copies.