Taking the Butler Research consultant quote in this piece from "The Register" at face value, one can only assume that IBM is basically throwing in the towel re. DB2 and its ability to handle XML :-) The excerpt below certainly implies this:

..So, using relational storage is inadequate for one reason or another, and IBM has concluded that another approach is necessary. The company’s next generation database will therefore have two storage engines: one relational store and one native XML store. And let me be quite clear about this: these engines will be completely separate, with separate tablespaces, separate indexes (Btrees and so forth on the one hand, and hierarchical on the other), and so on...

Hold on here! IBM only