OK, I didn't mean to get started down this route because I'm a little overworked, but I ran my contextual distance analysis on the Voynich graphemes (in EVA transcription). Based on that, here is my best guess at the Voynich vowels.
The following image shows a map of the similarity of the graphemes in the Voynich Manuscript. Like the King James genesis, we have a small island of five graphemes which occur with the word boundary (#). I will call these the *vowels (note the asterisk, which is my caveat that this is all hypothetical).
The *vowels, in EVA transcription, are the letters z, t, k, f and p. The Voynich graphemes represented here are:
There is an obvious graphemic similarity here: The tall, loopy letters are all *vowels, as is the z, which might be called a small, loopy letter.
Interestingly, the closest contextual similarities here are between the graphemes that look the most similar:
sim(t, k) = 0.88
sim(f, p) = 0.87
By contrast, the strongest similarities between any two vowels in Latin is sim(e, i) = 0.77, while in English it is sim(a, o) = 0.59.
If the *vowels are indeed the Voynich vowels, then I propose that we are looking at a script with only three vowels, and the EVA [t,k] and [f,p] are merely graphemic variants of each other.
Is it possible that the underlying orthography is based on something like the way Hebrew is used to write Yiddish, using the [א,ו,י] to represent vowels?
In fact, I'll go a step further, just so I can claim credit if this turns out to be true: Given my earlier feeling that this is a polyglot or macaronic text, is it possible that the underlying text is in Hebrew and Yiddish (or another language of the Jewish diaspora, like Ladino)?