1/ I wasn't citing Ts'o's opinion. I was citing his report on a meeting of several filesystem developers. He wasn't say what "should". He was saying what "is".
2/ The transaction rename semantics that ext3 provided were really a bug (or mis-feature or short-sighted design or whatever). I think it was only ext3 that provided it, certainly not ext2, probably not XFS, not sure about reiserfs. Any userspace that relies on it (without checking that the filesystem in use is ext3) is buggy.
That said - I think that it would be good if Linux did provide some transactional guarantees that didn't require fsync and that user-space could rely on across all filesystems. I suspect that enhancing rename would be a good start and could be done with little or no performance cost. It might even be good to provide something more explicit. But I don't think that 'barriers' is the right model.