The useful contribution of "the object model" is its ability to let users define their own -- and often very complex -- data types. However, mathematical structures known as "domains" in the relational model also provide this ability.
Therefore, a relational DBMS that properly supports such domains greatly diminishes the reason for using the object model.
Given proper support for domains, relational database models are quite capable of handling the complex data encountered in time series, engineering design, office automation, financial modeling, and so on.
Because the relational model can support complex data types, the notion of an "extended relational database model" or ERDM is "extremely inappropriate and inaccurate" and "it should be firmly resisted."
(The capability that is supposedly being extended is already there!)