If you don't have a device that can use Android NDeveloper Preview but want to use the update's new Quick Reply feature, there's a new app that'll help you out. It's called QuickReply. The app essentially emulates the feature by copying notifications that come from messaging apps. Expanding those notifications will bring up a text box for you to reply from, and it can send the content through to the apps as if it were a built-in feature. The app works for any device with Android 5.0 Lollipop or higher.