Welfare on 15 August 2014
I'd say 10 million would be too much of a gap. I am assuming Xbox One will be less than 20 million at the end of 2015 (but over 15 million), and predicting Wii U will be less than 15 million (but over 12 million). So a gap between 4-6 million is more likely.
Won bet with t3mporary_126 - I correctly predicted that the Wii U's LTD at the end of 2014 would be closer to 9 million than 10 million. http://gamrconnect.vgchartz.com/post.php?id=6673287
