The joke about Juggalo facepaint is both true and funny but I think there is some actual merit to that idea. Camo clothing (and I don't mean the kind you see everyone wearing at rural WalMartss) goes in and out of fashion every couple years. Military-style jackets, boots, and caps (think of a stereotypical anarchist style) are also perennially in style with certain crowds. I don't think it's too far fetched to imagine a future where camo facepaint becomes fashionable enough to be widespread, there's also a lot of artistic potential available in non-traditional patterns and colors.

I can't really see a way for AI cameras to get around properly applied facepaint, especially varieties that are IR absorbent or reflective. I hold the human brain in very high regard when it comes to pattern/symbol/shape recognition and if facepainting techniques are good enough to trick human visual processing, it's going to be good enough to fool any existing AI. For an example of what I mean by proper technique, refer to this video: https://youtu.be/YpzUr3twW4Q

The trick is in getting enough people to adopt such a strategy that you can't be identified through simple exclusion. I think the idea of camo/other facepaint isn't so foreign and unappealing as to never come into common fashion.