Why not simply make the pipe explicitly HTTP?

    first | second | third

"first" starts up a HTTP server, "second" is a HTTP client which makes a standard HTTP request to "first" declaring in the headers what content types it can support, and "first" returns a standard HTTP response declaring in the headers what kind of content it is sending. "Second" is also a HTTP server for "third" in the same way, and so on down the pipeline. All the OS has to do is coordinate a free TCP port for each pipe. The HTTP client can simply be a lightweight headless Chrome Electron bundle, and the whole pipeline gets all the benefits of HTTP (standard UTF-8 encoding, compression), with only a small overhead of cookie policies, cross pipe scripting, modern auth tokens, 2-factor authentication between client and server, SAML, and a tiny surface area increase for security concerns but only a few dozen MB or so.

Plus the pipeline then has ongoing two-way communication up and down it.