I don't see anything described that can't be done in a userspace library through shared memory. Maybe security is a concern, where we don't trust some nodes tha

I don't see anything described that can't be done in a userspace library through shared memory. Maybe security is a concern, where we don't trust some nodes that might be exploited not to be able to screw with the shared memory? But then zero-copy would be off the table for the same reasons, no?