Changes in Pre-Egyptian vocalism

Lately I've been reflecting on what Loprieno says about the early Egyptian vowel system on page 55 of Ancient Egyptian: A linguistic introduction (1995):

"In our discussion of phonology (section 3.4.3), we saw that one of the major features of Egyptian in its early stages was the presence of a strong expiratory stress, which eventually caused a reduction to /ø/ of short vowels in open syllables in posttonic position, with the resulting change from the Dreisilbengesetz to the Zweisilbengesetz (**saḏimat > *saḏmat 'she who hears')."

While Loprieno speaks of reduction to zero, I've long been thinking more along the lines of a Pre-Egyptian system of *a, *i and *u being reduced to *schwa* wholesale in all unstressed positions. To begin with, long vowels were only to be found in stressed positions in Pre-Egyptian, at least if the comparison with Proto-Semitic is trustworthy, and this length contrast in stressed positions clearly remained in Egyptian, as still evidenced by Coptic. I therefore choose to write all of these reduced, unstressed monophthongs of Pre-Egyptian as *a (to be implicitly understood as [ə]). Furthermore diphthongs *Vy and *Vw (*V = any vowel) then become *i [əj] and *u [əw] respectively. This has worked very well for me for a while now. The result is an Egyptian vowel system that still looks on the surface much like Proto-Semitic with long vowels restricted to stressed syllables and unstressed positions having only short *a, *i and *u. Yet since the system has been notably altered, we find a curious incongruence nonetheless between the vowels of Proto-Semitic and those of Egyptian.

We can also avoid a lot of the wildcard symbols Loprieno and others occasionally use in the unstressed syllables this way since my theory makes this pointless: Only *a can exist in these positions unless accompanied by a written semivowel y or w in which case the appropriate short high vowel is selected. It appears that the matter of whatever the original vocalism may be is an issue for Pre-Egyptian reconstruction, not Egyptian proper. Loprieno's */'ri:ʕuw/ (> */'ri:ʕə/) 'sun' becomes my *rīˁa.

There are further reasons why I'm dwelling on this, but I've divided it up into subsequent posts.