I think Linux is going in the direction of "everything is a dbus API" instead. Linux needs it's own "9P," or equivalently practical, if it wants to reverse this

I think Linux is going in the direction of "everything is a dbus API" instead. Linux needs it's own "9P," or equivalently practical, if it wants to reverse this trend. DBus, while perhaps not the best IPC mechanism, currently fills the gap. Several of the systemd binaries are there purely to shift from reading and writing files to pushing updates over dbus. See for example systemd-hostnamed.