This is no longer true. I have .IO domain for more than 2 years. 2 years ago, I remember the country for domain on Google Webmaster Tools has been "locked" to

This is no longer true. I have .IO domain for more than 2 years. 2 years ago, I remember the country for domain on Google Webmaster Tools has been "locked" to Indian Ocean Territory. But at least for last 6 months, I'm now able to change it to any country or leave it unspecified which indicates that .IO is now treated as generic TLD by google. The article you have quoted is simply out of date.