I'm not convinced spymark is better than just "invisible watermarks", spymark to my ears sounds designed to be sound very negative when invisible watermarks are not always negative, e.g. the counterfeit bank note example.

The article spent quite a bit of energy explaining why the word choice, seems like you're just ignoring that? Also, bank note watermarks are not invisible. Watermarks are not invisible, as the article (again) took pains to explain.

    Tech like SynthID I see a net positive especially since it doesn't degrade text quality.

It absolutely does. It constrains high-entropy word choice so it can "store" other things in your text. Your text actually has information removed from it.

    I dream about a browser extension running at all times that makes text more translucent based on the confidence of LLM writing.

Sounds very much not worth the anti-consumer, anti-privacy aspects which (again) the article explains.