Google will allow you to use Smart Replies from any messaging application
Limited to the Allo application, Smart Replies uses artificial intelligence to analyze incoming messages by formulating an appropriate response to the context we are in.
For example, when you receive the "where are you" or "what you're doing" message, the application could auto-formulate the answer "on the go" or "I'm fine", leaving the user to confirm sending it by interacting with the on-screen notification message. When the phone is set silently, or we drive a car, the automatic answer may be "sorry, I can not speak now."
However, certain messages or contacts marked as priority will be able to pass on automated messages, triggering alerts prompting an immediate response
Google does not detail which applications have priority for deploying Smart Replies. Perhaps the first recipient will be Google Hangouts, followed by Facebook Messenger, Skype, Whats App, Twitter, and other third-party applications