I managed to make changes to GLORP, regarding usage of single table inheritance and embedded objects:
1/ Now, while querying the abstract class, embedded objects from specialized subclasses actually get retrieved.
2/ Also, while querying the abstract class, it's now possible to use attributes from concrete subclasses in the where clause.
Too bad I needed to override a number of methods for this, though all tests are still green.
Would someone be interested in this? (iow, is it worthwhile to create tests, pull requests, ...)