What is your point here? You claimed that "other IPC solutions" _could not_ do this on top of sockets, but as I've shown and now you admit, you definitely _can_. Obviously I'm not suggesting you roll this by hand, nor claiming that a plain UNIX pipe is a fully featured RPC system; just that there's a million RPC systems out there that do it and don't need anything else than sockets.
I don't know what binder does exactly, but rendez-vous synchronization is surprisingly hard to do efficiently on POSIX systems without excessive context switches.
What is your point here? You claimed that "other IPC solutions" _could not_ do this on top of sockets, but as I've shown and now you admit, you definitely _can_. Obviously I'm not suggesting you roll this by hand, nor claiming that a plain UNIX pipe is a fully featured RPC system; just that there's a million RPC systems out there that do it and don't need anything else than sockets.