Many users started using Hangouts just after the SMS support feature. Conversations integration from SMS and Hangouts at one place made it more useful and simple to use.
There is no word from Google for the SMS support in Allo or any other app.
If you still plan on using Hangouts for chats going forward, make sure you've updated Hangouts to the latest version of over at Google Play or APKMirror.
Click below to Download the Latest APK update
Hangouts v20.0.1 APK