Yes you can create a full screen TWA easily with Discourse. @pmusaraj even added the .well-known verification json to a site setting in core so you need no modification on the Discourse side. Just fire Android studio and create your project.
There are also other ways, like automatic push of PWAs to employees home screen for Google Apps for Business, listing of PWAs in the Microsoft store and on the Samsung Store. We are tracking all PWA related news and will write guides about those as soon as they are available.