ArcGIS Data Store as many positive capabilities like portal analysis, big data clusters (optional), hosting of 3D Services.
ArcGIS is utilizing a PostGreSQL database embedded and encapsulated to provide many of these new capabilities. It would be usefull, if already other database management system exist, to be able to reconfigure all new kind of capabilities with an existing database like Oracle, SQL Server, etc.
Often there already is a concept and process to run the databases (recovery, backup, security-roles, etc.). To reuse this kind of enterprise - experience is the point of the idea. Reconfiguration of the datastore towards multiple-existing databases in an enterprise.