I'm fairly certain that devices in twenty or fifty years will still be able to play MP3. It's too pervasive and supporting it is too easy for it to disappear just like that. It might not be supported in hardware (like it is today in many devices to save battery life) but there will be plenty of software.
You tend to not be able to use formats because hardly anyone used them in the past. MP3 is too popular for that to happen. (As is JPEG, PDF and probably AAC.)
You tend to not be able to use formats because hardly anyone used them in the past. MP3 is too popular for that to happen. (As is JPEG, PDF and probably AAC.)