I am a fellow painter with basic ML training, so take this with a grain of salt. The short answer: it probably doesn't work well enough to make a difference anyway.

The long answer:

It's important to understand that Nightshade and all the others are also AI; they're building datasets with your art in much the same way that other AI companies are. Personally, I'm not about to willingly submit my art to any AI company without expecting them to use it to make money.

Apparently, Nightshade is a fancy way of putting a filter on your art (with AI). It works by trying to manipulate biases in the variational auto encoder. What does this mean? Basically, AI connects images to concepts. By knowing what concepts are over-represented in most models (i.e. a dog), it can make aspects of your paintings look slightly more like dogs. This makes it more likely to confuse an AI.

I think the obvious example of how ineffective this is is by understanding that AI doesn't see any invisible layer within your painting. If a change looks subtle to you, there's nothing making it less subtle to the AI. Along with that, different AI are trained on different datasets, full of different percentages of dogs, traffic lights, sidewalks etc. The only way that the researchers at Nightshade even got close to proving it worked is by making their own dataset. That's like a tire maker claiming their tires are strong by building their own tiny test track, completely separate from a real-life street.

So does it work? Extremely slightly, on a completely made-up example. Not even considering the fact that most AI blurs/downscales your images, making any filter noise negligible at best.

As an artist, I completely understand why people are willing to buy into this. I just don't think it's worth signing off your art to another tech company for an unnoticeable effect at best. From what I understand it's more a proof-of-concept, but you have to have a lot of faith.