It would be very useful if API could mark the values that have been “fallback” as the locale they have been fallback to. For example if I don’t fill the title and it fallback to a default locale, I’d like to know that on a data level.
A real-world example is for example for content that may be translated but it is not required to do so. In that case, we could display a warning for the user that “we apologize, but this is only available in default locale”.