Couldn't we just come up with some convention for "expanded filenames" where the meta-data is included in the file name itself? In the UI portion, you see what you see now, no difference, but say anything after the // delimiter in the file name is considered meta data and not shown in the windows/terminal UI.
Not sure if it's a good solution but if I were to put the meta data somewhere I would somehow try to put it in the identifier of the file (the name) as it is data that would help me identify the file AND it's content!
This is partially what filesystem forks/streams were supposed to be for. The big problem, as mentioned, is that this works for the OS, but isn't somehow transferred to third parties.
Not sure if it's a good solution but if I were to put the meta data somewhere I would somehow try to put it in the identifier of the file (the name) as it is data that would help me identify the file AND it's content!