Re: 500-year half-life?
"I'd be a little sceptical about the claimed half-life."
I wouldn't; the half-life of DNA is pretty well established and 500 years is used as a rule of thumb by most archaeologists. DNA can be extracted thousands of years after the death of the animal in question.
The density is interesting, but this is pretty clearly too slow for any practical use - even ultra-slow high density archival ops need a better R/W timecale than this. I seem to recall a similar idea 3-4 years back using crystal-based storage that was also hugely space-efficient and very, very long-lasting, but simply too slow to have any serious purpose. I can see it being used to, for instance, make some kind of 'golden disk' for strapping onto a deep space probe or something, or a knowledge super-archive buried under Greenland (like the seed archive) in case of thermonuclear war... but other than that, this is just a curiosity.