Nothing is impossible. Porsche already developped a SLK-type roof for the 996 and I'm pretty sure that someday it might be an option for the 996. But with the 996 sales going that well right now...
2004? If you're friend doesn't work for Porsche, he doesn't know for sure.
There is a lot of speculation about the next generation 996: V8, direct fuel injection, SLK-type roof, electronic brake system, etc. etc. etc. . Right now, it is pretty difficult to predict how the new generation 996 will look alike. Maybe we should wait to see how well the Cayenne sells. Based on Porsche's financial situation in a year or two, it is much easier to make forecast regarding a new 996 generation. Development of the next generation 996 has already started a while ago as far as I heard but I also heard that Porsche keeps themselves all options open, especially because the future world economics development is pretty unclear.
My prediction is that with the current flat six engines, its gonna be difficult for Porsche to offer new high power generations of engines which also have reduced emissions to comply with certain environmental laws. So the V8 might be an option, especially if the Cayenne succeeds and sells well.