Talvez como:
vicmd-accept() { prev_mode=vicmd; zle .accept-line }
viins-accept() { prev_mode=viins; zle .accept-line }
zle-line-init() { zle -K ${prev_mode:-viins} }
zle -N viins-accept
zle -N vicmd-accept
zle -N zle-line-init
bindkey -M viins \r viins-accept
bindkey -M vicmd \r vicmd-accept
Ou ainda mais simples:
accept-line() { prev_mode=$KEYMAP; zle .accept-line }
zle-line-init() { zle -K ${prev_mode:-viins} }
zle -N accept-line
zle -N zle-line-init