Yes, from what I have heard, the 2007 Navigator body will change with the Expedition. There will be a Navigator extended* version from what I hear, to compete with the Escalade ESV. Here are the match-ups for GM and Ford:

Expedition (non-EL) aganist Tahoe
Expedition (EL) aganist Suburban
Navigator (non extended*) aganist Escalade
Navigator (extended*) aganist Escalade ESV
*Extended of course is not going to be the real name of the Navigators longer version, I just dont know what they're calling it yet.

Hope that helped!