Innovations in payment technologies and the emergence of digital currencies [pdf]
bankofengland.co.uk
bankofengland.co.uk
The problem is who has authority over the validity of the distributed ledger. For Bitcoin, it's the biggest mining pools. The top one or two pools together have over half the hash rate, which gives them control. That wasn't the intent, but it's now the reality. Now we're back to a central trusted authority.
Not quite, though. It's possible for anyone to tell if the central authority is cheating, because everyone can see the ledger.