I’d be pretty surprised to find out that con-artists are a modern invention. But that’s just my differing interpretation and understanding of the world.
I’ll also throw out that when I was more of a practicing performer (“performance artist” was the closest word I used, and that was applied poorly), “cons” and “gags” were usually the words I used to describe the core of a given piece (or “modal event”).
In the context of a 600-hundred-year-old item I’d lean more towards “hoax intended to separate some nobility from their gold” than towards “crazy art experiment with no precedent or antecedants” (where “hoax” and “con” are interchangeable). We certainly have evidence of art forgeries subsequent to the Voynich, with Michaelangelo’s Sleeping Cupid. I’ve no citations prior, but would be surprised if cons had not previously existed.
That’s just how I oscillate around an axis, but callous dismissers gonna callous dismiss.
NOTE: I am not asserting that the V.M. is a con, just that it could be, and is more likely to be a con than an outsider artwork.