JDO is largely a functional superset of JPA, encompassing not only relational databases, but also object databases and key/value stores.
As there is no subproject of Spring Data that addresses JDO, I would like to see a new subproject of Spring Data, "Spring Data JDO". I think it would be better to keep Spring Data JDO separate from JPA and the other subprojects, as JDO itself enables support for most if not all of the database types addressed by the other subprojects -- it has been since its inception database type agnostic.
The JDO implementations supported out of the box should include, at a minimum, DataNucleus, the reference implementation for JDO.
By creating such a subproject, all data stores supported by DataNucleus and any other JDO implementation can be supported. For a partial list of the database types and database vendors supported by DataNucleus, see
The code from Hades (http://redmine.synyx.org/projects/hades) could be fairly easily forked and modified to support JDO.