V'zos Haberacha Theory

This is a followup to the excellent post yesterday by Bloghead about the history of Simchas Torah. A related topic that I have always found very interesting is the historical development of the torah reading on the 2nd day of Shmini Atzeres, which we now call Simchas Torah. In particular, while the source of laining "V'zos Haberacha" on that Yom Tov is in the Gemara (Megilla 31a), this predates by hundreds of years the earliest references to "Simchas Torah" and to the concept of finishing the annual laining cycle on that yom tov.

This leads me to conjecture that perhaps the original practice was just to lain part of V'zos Haberacha on that day - probably the first five aliyos which encompass Moshe's blessing - but not the latter portion concerning Moshe's death. This is also consistent with the fact that the original haftarah for that day, as per the Gemara, was Shlomo's blessing, the same haftarah (but one verse) as is read on the first day of Shmini Atzeres. And as pointed out by BlogHead, the day was originally called "Yom Haberacha"!

Another corroborating piece of evidence was pointed out to me by my father years ago: V'zos Haberacha, like all other parshas, is marked in chumashim - even to this day - with all seven aliyos. Yet if it was originally lained in totality only on the 2nd day of Shmini Atzeres, which can never fall on Shabbos, why would more than five aliyos ever be needed? Again, this implies that the original custom for the 2nd day of Shmini Atzeres was to read only a portion of V'zos Haberacha, and that the entire parsha was read on a regular Shabbos like all other parshas.

At some later time, the custom then developed of reading all of V'zos Haberacha only on the 2nd day of Shmini Atzeres, which became known as Simchas Torah. It's not clear what was then done to fill in the "extra" Shabbos that was thus freed up. Perhaps, as I once saw conjectured, Nitzavim and Va'yelech previously constituted one parsha, and were only separated at that time - which is why they're both so short!

Have a good Yom Tov!