I don't know how you plan on doing the VFS stuff on windows but back in the day when I still used windows (XP) I had a shell extension that let you tag a folder

I don't know how you plan on doing the VFS stuff on windows but back in the day when I still used windows (XP) I had a shell extension that let you tag a folder or file from the context menu. It would then be linked into a tag directory using either NTFS reparse points (aka junctions?) for directories or hardlinks for files.