No idea. But I don't think that's going to stop Microsoft. They also claim they've got several other patents which haven't been granted yet.

From the wording they seem to mean that you have to licence it if you use any implementation of FAT. But the patents they've listed specifically only mention having dual namespaces for files. If you look at some of the others it references then it begins to become very vague. IBM have patented the idea of munging long filenames into shorter ones. Microsoft have patented a Flash EEPROM updating mechanism in 5392427.

There is actually a Microsoft patent in there for an interrupt handler which runs in both protected and real mode...