Can LAAFU effects be modeled?

[magnesium]

There's certainly no harm in exploring that.  But since one of his goals is to "(b) consistently replicate these properties [ = 'well-known VMS statistical properties' ] when encrypting a wide range of plaintexts in a well-characterized natural language," I assume he'd prefer to model a system that would reliably produce LAAFU effects when applied to any source text.  

Just wondering: how difficult would it be to adapt the Naibbe approach from a unigram/bigram system to a syllabic "chunk" system?  Might the frequencies of different "chunk" types result naturally in something like the frequency distributions simulated through playing cards?

That is absolutely my preference. My first goal was to achieve something that could replicate word-level properties reliably and then build from there. I don't think it would be difficult at all to adapt the Naibbe approach to a syllabic "chunk" system, as the lengths of the chunks as you have outlined them—1 or 2 letters—are ultimately the single most important thing within the Naibbe scheme. The VMS's word length distributions and entropy strongly suggest that to reliably map something like Latin to Voynichese, a substitution cipher would have to be verbose, such that most tokens in the VMS stand for 1 or 2 plaintext letters. Within the Naibbe cipher, those tokens are randomly formed on a letter-by-letter basis—but by no means do they have to be. A "chunk" adaptation of the Naibbe cipher would essentially equate to a deterministic, nonrandom approach to plaintext respacing.

Even within a syllabic "chunk" system, though, I'm of the opinion that the cipher would need to be homophonic, with multiple valid Voynichese word types mapping to a given plaintext chunk. Otherwise it's hard to get the VMS's observed diversity of word types and frequency-rank distribution.