The vowel exchange "a" to "o"

[ReneZ]

Given the grammatical and figurative systems in the manuscript, what linguistic direction do you consider conceivable? I consider a Romance language rather unlikely, and I currently see nothing that would be typically Arabic / Hebrew or asian.

The question of which language could be conceivable, depends entirely on 'how this language would have been converted into the Voynich MS text'.
Most people will automatically assume some more or less elaborate form of character-by-character substitution. For that, all languages with regular consonant-vowel distribution will fail.

As soon as the substitution method starts deviating more from 'simple substitution', for example using lots of nulls, or a verbose substitution, all languages become equally possible, because the characteristic traces will disappear.

At best, it is an all or nothing situation.
In general, I would consider Arabic (which is a writing system used for different languages) or Hebrew a bit more likely, simply because these have not received anywhere near the same attention.