I think pretty much all modern file systems (including ntrfs and ZFS) have the facility to support this but it's more a matter of applications and operating sys

I think pretty much all modern file systems (including ntrfs and ZFS) have the facility to support this but it's more a matter of applications and operating systems taking advantage of it. On Linux for example you can set the user.mime_type xattr and it's possible to have Apache use that for it's mime-type.