IMO, if you're trying to figure out "equivalent megapixels" for a film format, you need to take scan DPI out of the equation, as it is more or less meaningless.

You could make a 100,000 DPI scan of a 35mm frame with an electron microscope, which would give you a 13 gigapixel file. But you wouldn't go around saying 35mm was equivalent to 13 gigapixels would you?