They are a fantasy only because users do not grasp the advantages of the RDM and confuse them with SQL, thus robbing vendors from any incentive to produce true RDBMSs.

If users are so accepting of denormalization as a solution to performance and are unaware of all its costs, why should vendors bother to come up with true RDBMSs that obviate the need to denormalize?

As long as users do not understand the RDM and its benefits true RDBMSs will remain a fantasy. Ignorance has never been conducive to progress.