The funny thing is that Boeing designed and sold an all-new MOM aircraft nearly 20 years ago. That was the 787, the original 787-8, which was touted to replace the 757 and 767, both of whose production was running down. There was the 777 and 747 above it, and the 737 below it. In the event the 787-8 quite soon became a mediochre seller, as soon as it (finally) entered service there were few additional orders, and production switched to the enlarged 787-9 and even larger 787-10, the latter certainly impinging on the 777 market.
Somebody in Wall Street is going to be asking Boeing serious questions on why this previous MOM aircraft turned out to be relatively unwanted. It does seem that in going for a huge Intercontinental range capability, which I'm sure looked exciting, they in turn reduced its attraction for the far larger Transcontinental/medium haul market.