4. New Features in Readline
j. New user-settable variable, show-mode-in-prompt, adds a characters to the
beginning of the prompt indicating the current editing mode.
If you don't want to wait, and aren't afraid of a little compilation, I've published patched versions of bash 4.3 and readline 6.3 to github that support this functionality.
#################### VIM ####################
# FOR MORE INFORMATION CHECK:
# https://wiki.archlinux.org/index.php/Readline
# TURN ON VIM (E.G. FOR READLINE)
set editing-mode vi
# SHOW THE VIM MODE IN THE PROMPT (COMMAND OR INSERT)
set show-mode-in-prompt on
# SET THE MODE STRING AND CURSOR TO INDICATE THE VIM MODE
# FOR THE NUMBER AFTER `\e[`:
# 0: blinking block
# 1: blinking block (default)
# 2: steady block
# 3: blinking underline
# 4: steady underline
# 5: blinking bar (xterm)
# 6: steady bar (xterm)
set vi-ins-mode-string (ins)\1\e[5 q\2
set vi-cmd-mode-string (cmd)\1\e[1 q\2
In command mode, the cursor is displayed as block.
In insert mode, the cursor is displayed as vertical bar.