I suppose you could profile your app, watching the syscalls it makes over a full cycle, and then build a stripped kernel with nothing but those calls implemente

I suppose you could profile your app, watching the syscalls it makes over a full cycle, and then build a stripped kernel with nothing but those calls implemented. Any drivers not touched would also be removed. That would not eliminate the syscall overhead, but it would certainly minimize boot time and improve security somewhat by reducing the attack surface.