I don't think it's possible to rule out Greek or any other language that is a reasonable candidate within the timeframe for the manuscript. If someone proposes a particular Greek solution, we could rule out that particular Greek solution for being inconsistent with known Voynichese properties. But we can't rule out Greek itself as the language.
This is because we know that if it is language (and not meaningless gibberish), multiple things have been done to the text to give it the myriad un-language-like characteristics that it has, such as the entropy issue, the line patterns, etc. We don't know what these processes applied to the text are, and until we do have a better idea of them, we can't rule out the possibility that they could make a Greek text look rather "un-Greek". And the same for other candidate languages.
In contrast, if a simple substitution cypher were the solution, we would be able to eliminate candidate languages very quickly.
This is because we know that if it is language (and not meaningless gibberish), multiple things have been done to the text to give it the myriad un-language-like characteristics that it has, such as the entropy issue, the line patterns, etc. We don't know what these processes applied to the text are, and until we do have a better idea of them, we can't rule out the possibility that they could make a Greek text look rather "un-Greek". And the same for other candidate languages.
In contrast, if a simple substitution cypher were the solution, we would be able to eliminate candidate languages very quickly.