Menahot 32: Elijah the Prophet and the Halitzah Shoe

On the writing of a mezuzah - in terms of the scribe's method of holding the parchment, leaving space at the top and the bottom, and so on. Including shifts in the application of varying views with regard to the writing of the text itself. How was that dispute resolved? The Gemara introduces the determinant of Eliyahu the Prophet -- in the non-mezuzah example of the halitzah shoe, and when even that determining voice would be accepted as law and when it would not: namely, as guided by the widespread practice of the Jewish people. Also, the sanctity of tefillin, mezuzot, and Torah scrolls - can tefillin parchment be "demoted" to be a mezuzah? It would seem yes, except for the requirement that the mezuzah parchment needs scoring. Plus, not sitting on a bed (couch?) that as a Sefer Torah on it.