MODx could get a lot of mileage out of promoting the xPDO stuff... write some really solid documentation (preferably run it by someone who isn't an expert in that stuff and see if they can stumble through it). Some videos would be a godsend, and I'd suggest using more clear names... lord, xPDOObject doesn't tell me a thing about what the heck that object is or why I'd want to extend it. Little things like that just make it more difficult to understand.
It's an xPDOObject, so it is providing what ever user-defined class you want to build with xPDO access to all the methods it provides. This is much like PHP's stdObject, though every object implicitly extends stdObject in order to gain access to it's methods, whereas xPDO requires that your classes explicitly extend xPDOObject. As I said in the other topic, nothing good documentation won't cure...
What I'd love to see in MODx is the ability to define arbitrary tables... e.g. "Store Locations", and then the manager could control the CRUD access to edit/update the address, city, state, and phone fields. You can emulate this with Template Variables, but it's not 100% clean when it comes to the database architecture. Expression Engine offers more flexibility there, but it's not all that clean either. A GUI front end for defining table relations would just be amazing... I've only really seen it in Filemaker... ha.
This is the vision, to have visual and programmatic editing and lifecycle-maintenance tools in MODx/xPDO for user-defined domain models reverse-engineered from existing databases and/or generated along with new custom database designs, in a way that makes it easy to develop and maintain applications, manage data structures and relationships, and even share data across various storage engines. We're only part of the way there, but hopefully, what we've done with xPDO already (i.e. developing MODx Revolution 2.0, and other projects that we'll hopefully be able to turn into case studies) will attract the attention of enough PHP developers, UI designers, and technical writers, and others interested in contributing to the effort to make that vision a reality sooner than later.