POSIX outlines vi mode, but emacs is not mentioned.

"vi - Allow shell command line editing using the built-in vi editor. Enabling vi mode shall disable any other command line editing mode provided as an implementation extension."

https://pubs.opengroup.org/onlinepubs/9699919799/utilities/V...

Fair fair. I guess the most important thing is that you pick one style of efficient command line searching and editing and run with it.