See https://github.com/fish-shell/fish-shell/issues/3164#issueco... for incomplete but large survey of NUL flags.

Takeaways: (1) There is no consistency in flag names, even --long ones (2) impressively many tools do support it! Note that some affect only input or only output. (3) All do NUL-terminated, not NUL-separated. That's fortunate — matches \n usage, and gives distinct representations for [] vs [""].