I think there is a great potential for highly interactive predictive suggestions like shown under section 2 "discoverability" in the wider Unix ecosystem, however discoverability is the key issue, and a massive problem space. Command line programs are black boxes (they could be pure bash, a compiled C++ binary, an npm package, etc), which means there is no programmatic standard for extracting the command set.
The most backwards compatible format to achieving this would be a interface like abstraction on top of regular binaries (similar to the concept of TS interfaces adding type completion to JS) which describe a list of parameters/flags and their valid values/data types with an associated description. I think a system similar to this gives an intuitive and extensible suggestion system without requiring inconceivable redesigns to existing systems whilst maintaining the familiarity and ease of use of the regular command line.
The most backwards compatible format to achieving this would be a interface like abstraction on top of regular binaries (similar to the concept of TS interfaces adding type completion to JS) which describe a list of parameters/flags and their valid values/data types with an associated description. I think a system similar to this gives an intuitive and extensible suggestion system without requiring inconceivable redesigns to existing systems whilst maintaining the familiarity and ease of use of the regular command line.