
In these days there has been much fuzzing about the new browsing with files organizing themselves with the help of meta data. Maybe you ask yourself "What have this to do with the spatial browsing in gnome and how can it improve the browsing?". That's what I did. As I see it, the gnome people have introduced the spatial browsing so we are used to it when this new browsing is coming to town. This is very intelligent move of the gnome people and will help us adopt faster to this. This is when the spatial browsing is really making sense. I hope you see this when you've read this article.
Assuming, of course, that you used only those applications that were aware of these special features in the operating system. And that you didn't need to access your data from another environment (such as over a network file system).
Yes, it wouldn't be possible without the interaction between applications and filesystem.
In theory it would be possible to transfer the associated stored metadata of a file over a network, e.g. transformed into an 'XML-attachment'. But of course the counterpart would need a filesystem and applications that are also capable of using this informationen. If you think this is far fetched then think of something similar to an MP3-ID tag, this is also a form of standardized metadata which can be transfered over different kind of networks or computer architectures (x86, powerpc, sparc etc.).
Of course applications would have to be modified to use these features.
The additional needed space is IMHO not that much of a big concern. Not only get disk bigger and bigger and that trend isn't about to change or to go in a reverse way. You could save much space by doing diffs between file versions (like cvs or subversion) and delete the oldest file and only keep the latest version as a full set.
However I agree with you that it will need more ressources (disk space, cpu time etc.) in total than todays FS. So storing temp files on such a filesystem wouldn't be a good idea, but afterall it's just a dump vision of mine (for now) ;-)