Roku should consider creating a generalised internet radio streaming app, with an ability to input details of any internet radio stream along with a library of popular streams from major broadcasters. Precedent: similar to the Roku media player app.
The radio app could have a screen layout similar to the Roku home screen with a space for adverts on the right hand side. Roku could sell that advert space for revenue.
If not an channel app, maybe extending the current home screen to have a radio menu with the ability to add shortcuts to popular stations