cool idea! In fact, if you could make it optional that the inclusion of such notes in an export appeared as footnotes, perhaps as an item attribute.
If the attribute was not checked, then the item notes could appear inline with the text, perhaps with delimiting lines above and below
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something like this
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If the item attribute was checked, then the note would appear as a footnote (1).
Regards,
Bal
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(1) something like this