There are IPC mechanisms today which aren't just bytes. For example, the ability to send file descriptors over unix-domain sockets. Strings of bytes fundamentally can't do that. And in programs that pass file descriptors, it doesn't require any ghostly assumptions about what namespace the strings need to be resolved in.

To be sure, Unix-domain sockets aren't the answer to everything, but they are an example of a different way to think about communication.