It's not very possible, because Vim is a modal editor, whereas NSTextView widgets are not. But if you want, you can try to approximate some vim bindings by using modifier keys and leaving it non-modal.

If you come up with some good vim approximations, let me know and I'll add them to my page.

Vi keybindings exist for the bash shell, a user enter inserts mode by default unless they hit esc to go into command mode for whatever reason.

I don't see why a keybinding couldn't be designed that emulated this functionality.

Because Cocoa text fields are not modal. The original poster already told you why it is not possible to do this within the context of the Cocoa classes without doing more programming than mere configuration.