Though all the sub-pages of that state things like “[This structure is valid only for version 3 of NTFS volumes; it may be altered in future versions.]” — while it is true that any API could see breaking changes in future, this suggests that you should expect them, so I'd not call it supported in the same sense of the main file/directory access APIs which I would not expect to see breaking changes in (additional properties & functionality yes, but not existing things changing behaviour).