Three passenger versions have been sold but they're Boeing Business Jet's so we'll never know who ordered them.
"The new orders included two VIP passenger versions of the new 747-8 derivative of the jumbo jet and also a VIP version of the mid-size new 787. The tally also included two 737 Boeing Business Jets, which are standard VIP jets."
http://seattletimes.nwsource.com/html/businesstechnology/2003290459_webbdigboeing05.html?syndication=rss
Pretty sure 1 other was sold earlier this year.
It's probably for head of state aircraft for some country. It's pretty hard to hide something as large as a 747-8I. I bet several people will have pictures of them posted on websites, and we'll know who bought them.
Highly likely to be Middle Eastern governments such as the UAE, Qatar, Oman, or Saudi Arabia as well as the country of Brunei. All of them fly a large number of luxury aircraft including 747SP's.