I think this is different because I'm full on opening an instance of vim. (I didn't know about GNU Readline though and it looks awesome - I'll definitely try and work it into a project at some point).
Either Readline let's you do the same, or that is just a bash specific feature I am miss remembering. I can check later when I'm not on my phone.
I'm only using GNU readline for my bash prompt, but if I press v it spawns a full-on $EDITOR instance to edit the commandline.
This is awesome (I still have a lot to learn about bash) and effectively what my module does.
Just so others know, you have to put bash in vi mode and press Esc before v (otherwise it's ctrl+x ctrl+e).
set -o vi
Aye, looks like I was wrong. This is a feature that bash has, not Readline. (in bash 4.2: bashline.c:858)