On plain texts and ciphers (a thought experiment)

[-JKP-]

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Is there anything in Voynichese that argues against this?
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It depends on whether or not you consider the word breaks as natural breaks.

If you assume they are, ask yourself the question, "How many natural languages have certain letters that occur only at the beginnings or endings of words and never (or almost never) anywhere else, compounded by the fact that certain letters occur only in the middles of words and never anywhere else?"

You also have to ask yourself whether any of the characters are null characters. Unless the subtle differences in letter shapes are representative of different letters, the alphabet is very abbreviated, about 17 to 20 common characters depending on how you evaluate them. If you then assign some of them as nulls, the alphabet becomes even smaller. It would be difficult to represent a natural language with so few sounds, unless it were an abjad or some similar system.

You also have to account for the very high level of repetition... not just when the same words are next to each other (which might happen in poetry or lists) but the high level of similarity of letter order in words that occur frequently.