The thing about FLAC versus some other formats is that it is 'open-source.' What's under its hood isn't a secret, unlike the Apple and Windows formats or MP3, so baring some Great Simplification, a future culture that can deal with digital media will (hopefully) have all the info they need to reconstruct the data. That's not an argument for using it, but it does make the decision practical. Someday, Microsoft and Apple will be dust, and who knows what will control their ip?
Another subtlety to this subject is that all of these file formats are alternate ways of describing the same thing. With lossless formats, it isn’t really correct to think in terms of a generation. A FLAC version of a WAV file is the same information, expressed in a different way.