From my modest point of view, the JCR API represents a completely new architectural layer, and this statement is true for most types of applications, not only for CMS. Let's have a look on what JCR is *not*: it is not a new middleware such as JDBC, or a persistence abstraction such as EJB3 or JDO, nor a OR-framework such as Hibernate or Toplink and much less an actual data storage.