This will happen, but not until the OpenXML file format ratifacation is completed. Why build file compatability twice? MS will have to change the default formats in Office 2007 and the free filters.
Reading 2007 files is a fact of life. I have tried to stop the use of 2007 internally and have succeeded through IT policies. Unfortunately, customers and business partners do not respond to our internal policies. As time goes on, more and more people will be sending files in 2007 format and expect you to open them and edit them.