I can see the flexibility demands that a rapidly changing data model requires. But I will argue strongly against abstracting the data model away from the database layer.

All these conceptual thought games around changing data models, software changes and end user configurablity just pass the decisions in a changing application to a person that is abstracted from a relational view of the performance impact of the data model change they are contemplating.

Unmanaged incremental performance risk with potentially cheaper development blind to the risks of the modelling decisions they are making. If only I could force the decision makers to do the ongoing support for these applications.