Would you prefer I rename the module to make it clear that it is not generic (to something like 'notify_last_command'), or that I add support for generic notifications?

For reference, I don't think it would be that easy to decouple the notification functionality from the notify-if-not-focused functionality (on Mac OSX, additional flags are needed to specific a callback to focus the window, etc). However, it might not be too hard to add support for arbitrary notifications and then offer a setup function to enable notify-if-not-focused.