Not sure how reliable this is, but this blog post on boarding area predicts a 3-3-3 config on United's 787s based on their officially announced seat numbers.
http://boardingarea.com/blogs/thewan...-787-seat-map/
I think this would be a great opportunity for AC to introduce an E+ product. If they really want to do 3-3-3 in the back (32" seat pitch?), then do a few rows of 2-4-2 with 34". The additional revenue in E+ should make up for a few less seats.