If only you understood how FDD's work, Sellam!
You say "> A floppy diskette is a stream of bytes. "
The stuff on a diskette is not a byte stream. It's a carefully worked-out
bit-oriented protocol written in a self-clocking modulation scheme with
in-band signalling encoded in, among other things, missing clocks. There
are write splices before and after every sector ID and before and after
every data + crc field, during which byte-synchronization (framing) and
bit-synchronization are lost completely. That hardly qualifies as a byte
stream. That's just another reason some other, perhaps less
synchronization-intensive data transfer mechanism should be used, IF what
you really want is an archive of the bitwise pattern of flux reversals on
the magnetic medium, then you have something you can store, and that you can
recreate with an appropriate drive interface.
You'll have trouble including header information on such an arrangement,
though it's possible enough.
However, as I've said before, a mechanical system is always destined to be a
headache. Some form of relatively non-volatile solid state storage is what
a modern archive needs. Maybe CD is adequate, but who knows how long that
fad will last. In another decade, the multiples tens of GB you can store on
a CD/DVD may not be adequate for then current computers, though it will
probably always be suitable for this purpose. If there get to be such
things, a multisession DVD might be just the thing. With as high an error
rate as FD's have, they're just not the best bet.