Hi, I have several smart speakers in the house including Sonos, Alexa and only one Chromecast device. I think Sonos and DLNA/UpNp is necessary if you want the app to remain viable in the short to medium term for those people who like to use other apps than the stock Sonos/Alexa apps (which are dire for music playback)
@Jon Kingsbury DNLA “casting” is a planned feature, but no deadline set. DNLA blocker is that straightforward support for it will require doubling Poweramp APK size (+10mb) for the feature which I guess will be used by few percents of users (good if by 1%). Poweramp recently moved to Play bundles which allows “feature” download, so main APK may stay small and additional features are downloaded as needed, but there is still an issue for website (uni) builds.
As for Sonos, there is no open AP