Voynichese is a numeric cipher?

[Mauro]

Overall, you’re right that a person is capable of anything, but it’s important to understand that, taken together, creating a single book cipher is incredibly difficult. And if we’re talking about a cipher (which means we’re implying the purpose of encryption), then we come to the point that complex ciphers are impractical to use because they’re redundant.
It’s the same as if you were preparing a culinary masterpiece for breakfast. You may want to do it, you may be able to do it, but your laziness will convince you to order a pizza...

Yet the fact is that many people still choose to create culinary masterpieces for breakfast. Some dedicate their life to it. 

One hypothesis I think is at least plausible is the VMS is the manuscript equivalent of a folly, for example the You are not allowed to view links. Register or Login to view.. A lifetime of work for no apparent purpose (but which I presume gave a lot of personal satisfaction to the builder). It's weird, thus improbable, but it exists nonetheless.