SSAS and other cube (MOLAP) tools create persistent cubes as materialized views. Databases that do ROLAP processing create "cubes on the fly" which persist for the duration of the query.

If PG adopts a materialized view that supports controlled automatic maintenance, then you'd have something similar to what the MOLAP tools do.

Note that MOLAP is a trap of sorts (no pun intended).

What makes MOLAP a trap? I'm only generally acquainted with cube analysis.

Apart from the complexity of cube updating, why do you say that?

You could before. The benefit of OLAP databases and other analytical engines is only partly due to the focus of the query languages. Storage format, and calculation engine requirements are vastly different between OLTP and OLAP.

While the constructs in the linked article increase the expressive power of SQL, they are more icing than cake for an OLAP load.