MP3s have been on the way out for a long time, being replaced by music subscriptions. And "MP3 player" is a feature of other devices, not its own device. Both my Apple Watch and Garmin watch can store and play MP3s without a phone; both also support music subscriptions.
The only market is in the "enthusiast audiophile flac player thing that costs way too much", just like it is currently for vinyls and DVD players.
The only market is in the "enthusiast audiophile flac player thing that costs way too much", just like it is currently for vinyls and DVD players.