One of the most important decision facing Boeing is what to do to respond to the A350. Specifically, what will Boeing's answer be to the A350-900 and the A350-1000. The A350-800 is sized for the 787-9 market (both carry roughly the same number of passengers).
Airbus is targeting the 777-200 sized market with the A350-900 and the 777-300ER market with the A350-1000. Boeing is waiting to see what Airbus does with these two models before deciding on a future improvements on the 777 or an entirely new model in this class.
From my discussions it seems that Boeing is leaning towards a package of extensive improvements of the 777 line. These improvements may include weight saving measures throughout the aircraft, a new composite wing, an external re-profiling of the exterior lines and improvements in the GE90 using experienced gleaned from the GEnx program. The last proposed improvement is addressed by Saj Ahmad in an article he wrote:
Engines May Hold Key to Future 777
At the end of the day it does seem that Boeing is in the driver's seat because it can respond to the threat of the A350 with a lot of flexibility.