When Office 12 debuts next year, the default 'save-to' file format of the applications will be XML. Or at least a version which Microsoft is calling Microsoft Open XML Formats.If Office 12 actually uses well documented file formats without intellectual property entanglements that other applications can readily and safely read and write, I'll (at least) chew my hat. File format control is so fundamental to Microsoft's business model this would only make sense if they are planning a radical transformation of their business model.
It does make sense if Microsoft plans to move to a 'rented software' model rather than the current no expiration 'licensed model'. Since I believe they very much want to move to a rented software model this move is not utterly inconceivable. So I'm only promising to chew rather than eat my hat.
BTW, Microsoft promised XML file formats for Office XP, but the implementation ended up being very proprietary and basically useless. This implementation resembles the OpenOffice file design: ascii XML with binary objects embedded in an enclosing zip file. Apple does something quite similar with their Office competitors.