why not use .xml(or .msoffice) as unified file extension of Office(includes Word ,Excel,PowerPoint,etc).
then we are able to open and edit the .xml in the unified IDE(office , just like Visual Studio IDE ).
That would defeat the point of filename extensions under Windows. VS is an IDE, yet there's absolutely no need for all the files it handles to have the same filename extension. It would be a nightmare for your average users to understand.