Following countries allow you to cash out Bitcoin tax free, if you're an early holder: the UK, Ireland, Cyprus, Malta, Belgium, Netherlands, possibly Germany, Switzerland, Singapore, the UAE, Monaco, the Channel Islands, Andorra, Italy (if you pay a €100k levy), Portugal, Singapore, and I probably forgot another dozen countries. Pretty much half of Western Europe.
If you have the money, most of these countries offer great quality of life. If you're sitting on a $100m gain.. it's worth it. A change of scenery isn't always bad in life. Personally I would never voluntarily pay 20% on a massive gain if there is a legal way to avoid it.
I guess what this article is implying is, since the US treasury does not know of the existence of these Bitcoins, people can easily renounce (committing US tax fraud in the process) and cash in.