It might, but it will still have to to deal with files going in and out of the system to other non-Longhorn computers (or maybe it just won't. Could be fun). This of course what holds back advancement in this area for all platforms (and is why Apple has pretty much abandoned type and creator codes on MacOS X much to the consternation of many long-time developers).
BeOS had a nice system where incoming files would be checked for magic bytes indicating the file type and falling back onto extensions. It would then store the MIME (like email attachments) file type in a file attribute (BFS has indexed file attributes). NTFS has file attributes (or are they just those alternate file streams?) and I'm sure whatever WinFS adds onto NTFS would be capable of storing this. We shall see.
IIRC the Linux desktop file managers work similarly to BeOS but just check the file type or extension on every opening as they have nowhere convenient (ie: LCD) to store the MIME type.
XFS supports attributes (but not indexed). I have a design for a "just enough to show how nice it could be, and ignore the tricky legacy/interoperability problems" level Linux desktop shell using XFS, LUFS (a Linux file system kernel module that forwards all of its calls to a user mode shared library via Unix Domain Sockets), Python and Qt percolating in my head. We'll see if any of it ever makes it to "actual code".