For what many are calling the "Super-Efficent" Boeing jet, which will probably be called the 787 (Lucky Asia 8), I think it should be a Boeing replica of the 330. 2-4-2 in Coach, 2-2-2 in Biz and a more spacious 2-1-2 or 1-2-1 in First.
Its interesting because current operators have a 2-2-2 first and 2-2-2 biz, with just a legroom difference. The 330 is narrower than the 777 but a lot of 777 operators have done away with the 2-2-2 Boeing configuration, and put in the 1-2-1.
Additionally, they should keep the raked wingtips instead of the regular winglets. LD-3 containers should be able to fit. Cockpit should have commanality with the 777 line to have more competition and help airlines (such as CX or AF) who already have 777s, go away from the 330 and to the 787.
Anything else which should be added? Comments are welcome.