They've implemented plenty. Their native token is being used on their blockchain, with their native wallet. It has withstood a $20 billion bug bounty via the hostile open Internet so far. They have a long way to go, but make regular progress reports. They started from scratch, unlike many projects which were a fork from pre-existing code, so they have done a lot to get this far.
RE: Peer Review of Cardano's Ouroboros