io_uring enables applications to submit multiple syscalls at once, and eBPF allows arbitrary execution inside the kernel!
https://thenewstack.io/how-io_uring-and-ebpf-will-revolutionize-programming-in-linux/
miniblog.
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Emacs as the init process: https://www.informatimago.com/linux/emacs-on-user-mode-linux.html (now that Emacs has an FFI, you could implement the missing syscalls!)