I use the Bixby key on my Samsung as a convenience key. Using a third-party app (bxActions), I have a short press mapped to play/pause like BlackBerries had, and a long press mapped to the flashlight.

There is also a hidden API permission you can grant using ADB that allows for long-pressing the volume buttons to skip tracks. I use this APK for that: https://github.com/Incineroar/skipTrackLongPressVolume