A hypothesis on why/how the VMS was made

[ololololo]

What I'm getting at is closer to Friedman's take after his ~40 years on this, an invented notation system, not a natural language with abbreviations bolted on, and not a straightforward cipher either.

Would a medieval doctor need such a system? Why would he invent a rather complicated system of abbreviations from scratch (if you don't think so, try it yourself), when he can encrypt or write in a lesser-known language that he knows? There are also no historical candidates for such a system of abbreviations.
Voynichese may be an artificial language (as Friedman said), but it is not a "conlang" in the usual sense. At the very least, it was impossible to communicate on it.

On Constance and Hus, I connected it to the Constance event since it was a major event for physicians in the region, and I thought that was an interesting reason to motivate a doctors guild to invest a large amount of money into something like this.

It can't be said that a lot of money was invested in VMS. As for the materials, they were all quite cheap and common, the parchment was of poor quality, and, if I may say so, so was the scribe also 

If that's already been looked into and ruled out, I'd genuinely want to know, since that's the part of this I actually care about being right or wrong.

I do not know about this myself. I've never spent any time in the Constance Archives in my life , but it might be worth it... It would be nice to find something similar, not necessarily identical.