I think Tanenbaum will win the argument in the sense that the way high-security OS kernels will be written will look like programming a microkernel, but when yo

I think Tanenbaum will win the argument in the sense that the way high-security OS kernels will be written will look like programming a microkernel, but when you look at what the hardware actually executes it'll look like a monolithic kernel. As an example, think of how Rust treats thread communication. The API looks like you're passing messages, but the whole data isn't being copied when you send a message, you're just sending a pointer. The compiler keeps track of making sure ownership rules are respected. One of the nice things about using a message passing API internally even if the implementation is just single-address-space shared memory is that if you really want more security you can change the implementation to be one where actual message passing takes place, and threads are isolated into separate address spaces like you would do in a proper microkernel. Whether you turn that on or not depends on whether security or performance are more important for your chosen application. It would be much harder to convert something like the Linux kernel into a microkernel.