1) Standardize on some structured text serialization format (I like YAML for this)
2) Write a new shell
Both of these things are compatible with the Unix Philosophy™, and thus said Philosophy is nowhere near collapse. Rusty around the edges, sure, and maybe with some asbestos in the ceiling tiles, but certainly renovatable.
The philosophy is already prevalent in the world of "microservices"; an application is split into a whole bunch of independent (usually containerized) programs communicating via something like JSON over HTTP.