The readline(3) manpage lists these four (vi, vi-move, vi-command, vi-insert) as possible options for the
keymap setting. I have tried setting these different options and they seem to have no effect beyond what
set editing-mode vi does.
Probably the most succinct way to answer this question is to give an example of how changing
keymap makes a difference.
Quote from the manpage:
keymap (emacs) Set the current readline keymap. The set of legal keymap names is emacs, emacs-standard, emacs-meta, emacs-ctlx, vi, vi-move, vi-command, and vi-insert. vi is equivalent to vi-command; <<snip>>