What if it's a "Lossy Encoder" for 15th-Century Latin?

[Rafal]

my current working hypothesis on this idea is that that the glyph strings are not linguistic

Not linguistic or not phonetic?

If  Voynichese "words" mean things like leaf, flower, star or water then it's still a language. 
You may not read them loud as folium, flos, stella and aqua. You may not read them loud at all. But they remain words from some language.

Even if they mean things like "with water" or "from leaves" then they are still language. Such composite words are typical for agglutinative languages.

Of course it could be not existing language but constructed language. If I understand correctly that's what you are suggesting.

That's theoretically possible but I see several problems with it. If you develop your ideas further we could discuss it more.