Having an airplane line-up from the 737-700 to the 777-9X means you have a complete twin engine travel toolbox. Airlines can carry two different types of tools in that toolbox. The Airbus Tool or the Boeing tool. The most efficient or easiest tool is often grabbed in a subliminal reach when accomplishing a mission. The latest Boeing tools will be the 737 Max, 787-10 and the 777X family of aircraft for an airline's toolbox. Airbus counters with a long list of NEO themed aircraft.
This is a focus is on the 787-10 and who will reach for it. The 787-10 will not go as far as the 787-9 nor will carry as many seats as the 777-8X. The seven thousand mile range is the size of the 787-10 tool. It doesn't go as far the A350 family, but resemble the range of the A330-900. However, it will outperform the A330-900 in its metrics for economy and capacity. People who buy the A330-900 already have the Airbus blood in its corporate veins. Asset bargain value airlines may order the A330 but the future would suggest the 787-10.
The 787-10 niche compliments the 787 family while it retires the smaller 777-200 Boeing type. It's presence in the 787 family causes an extended synergistic role for knitting the aircraft family ties together. Fleet commonality is the most important selling point for "bridge" models like the 787-10. Another "Bridge model” missing in Boeing's lineup, and is hurting single aisle sales. It needs a 757 replacement model. The upgraded 737-900 Max did not fill the Boeing "gap" in spite of Boeing's 737-900 confidence.
The "You complete me" theme is imperative for Boeing amassing marketplace synergy, and hopscotch over Airbus. The end of 2016 will solve Boeing's reluctance because it then can free up the resources for the follow on MAX extender.
Yes the 787-10 has a spot energizing the mid-wide body Boeing suite of aircraft. It allows airlines to fill its skies with sensible sized dual aisle twins. It Completes Boeing. Who will buy the 787-10 is a question easily answer by what airlines have already bought the 787-10. Asianic operations have filled the 787-10. This is a perfect aircraft for China the Gulf States and its neighbors.