Okay, first post here - I found this topic so interesting that I had to get an account to participate.
First off, Maknas, thank you for a truly interesting discussion/analysis of Hebrew morphology (I found the software and disease examples particularly interesting). I've always been aware of the fact that Arabic and Hebrew were very similar languages, I don't think I'd ever realized just how similar they were until I started reading your posts.
In any case, two little nitpicks about the origin of segolates:
*melex might not have been the best choice for this specific explanation, as the Arabic (and I believe the Akkadian) cognate, malikun already has a vowel between C2 and C3. I believe *kalbum (dog) may have been a better choice. Actually, the fact that both types of nouns seem to function the same way in Modern (and I'm assuming Biblical) Hebrew is a testament to the power of sound change and the force of analogy in semitic languages.
The (masculine) nominative plural ending for PS was probably *-uuma or *-uum. This is based on classical Arabic's ending, -uuna, and Akkadian's ending, -uu. The oblique ending was probably *-iima or *-iim. Again, this is based on Arabic -iina and Akkadian -ii. As you can see, the Hebrew plural almost certainly derives from the oblique form (if you already knew this, please feel free to call me an idiot). The final -a* may have never existed; so far as I know, CA is the only language it's attested in, and there it may have simply been inserted to conform to CA phonological constraints (a word can't end in an extra-long syllable). Even if it was there, it probably had very little to do with case.
Again, these are silly little nitpicks - feel free to call me a jerk for pointing them out/disputing your analysis.
What really struck me about these forms and indeed, many of the other changes in Hebrew you describe, is how similar they are to the changes that happened to many modern Arabic dialects.
An example from my own dialect:
CA: kalbun (dog)
kalb (loss of case ending - seem familiar?)
kalib (epenthetic vowel breaking up final consonant cluster - eerie, isn't it?)
This has the net effect of making malik and kalib look exactly alike in Arabic too.
Unfortunately, I can't give a plural example, as it's a broken plural. Actually, for the life of me, I can't think of *any* word of the types CaCC/CaCiC with a sound plural (not to say there aren't any). However, watch what happens to the active participle of 'KL (to eat).
'aakilah (loss of case endings/final unstressed syllable/vowel)
'aaklah (unstressed syllables disappear)
'aklah (long vowels shorten before cononant clusters)
of course, as per Hebrew, that (t) reappears in the construct state.
'aakiluun (loss of case endings/final unstressed syllable/vowel)
'aakiliin (plural form transitions to oblique with the loss of case)
'aakliin (unstressed syllables disappear)
'akliin (long vowels shorten before cononant clusters)
Okay, that ended up being far longer than I intended. Out of curiosity, will these fora explode if I post using unicode IPA/latin extended?