To make that happen, Microsoft is turning to what some analysts say is a risky strategy. The company is adopting Extensible Markup Language (XML) as a second file format in all Office applications, to enable better data exchange between the productivity suite and back-end software, such as databases. This "opening up" of Office could end Microsoft's lock on document file formats that have boosted Office sales in years past and made the software the de facto standard for desktop productivity.
So, for what that's worth. Second file format, in the tradition of RTF, probably. No one will use it unless requested to.