Brian, the goal of universal and pervasive metadata is a worthy and noble one. The problem is how to support non-metadata aware formats (like TXT or GIF) and how to support moving files between diverse filesystems.
To solve the first issue, you could say that, for TXT, you could store extensible metadata in the index, but that means that information about that file is now not attached to the file anymore and a rebuild of the index would destroy all the metadata.
Regarding the second issue, attaching metadata to an NTFS alternate data stream would bind the data to the file, but it would be wiped out when moving the file to a non-NTFS system, like a CD/DVD or a OSX partition.
It's a really tough problem to be resolved while keeping in mind backwards compatibility and portability.
I understand the problems involved, I just hope its something Microsoft is interested in working on