You're right, for the most part. We have to have hardware that doesn't lie when the data made it to disk, whatever that disk is. And we also need hardware that

You're right, for the most part. We have to have hardware that doesn't lie when the data made it to disk, whatever that disk is. And we also need hardware that can do atomic updates to single sectors. But once we have those things, and people are demanding them more and more, a copy-on-write filesystem should be perfect for emulating transactions, using that single sector atomic update to "commit" the transaction.