There was a discussion about that here about four years ago. I get the container / codec discussion, but I think this can be ignored in 90% of the cases. And I think we all agree, that it would be a big plus if JUCE would be able to create mp3, mp4, etc. files without having to worry about licensing issues. Are there any plans to implement this in the not too far future?
In the meantime, maybe you could add AudioFormatManager::getWildcardForWritableFormats() and AudioFormatManager::getWildcardForReadableFormats() - because in the current state those are obviously not the same as AudioFormatManager::getWildcardForAllFormats().
PS.: My current focus is on macOS, so CoreAudioFormat::createWriterFor() would be my personal preference.
PPS.: discourse is complaining about the title “CoreAudioFormat/WindowsMediaAudioFormat::createWriterFor() is not implemented” as not being descriptive enough