There'd be a whole heck of a lot more 3-3-3 Y cabins, for sure. I'm already super bummed at the proliferation of the A350 in Y - it's great upfront, but the A330/767 are much better experiences with their extensive 2-seat sections.
The 787 was designed to be 2-4-2 like the A330, but airlines figured out they could get away with stuffing another seat in across, making it a pretty miserable ride in the back. It's a fine airplane mechanically and fun to fly in the pointy end, but I'm in no rush for Delta to adopt it wholesale.
That said, DL does need a long-and-thin solution to make hubs like SEA work at full strength. I'm not saying a 787 style plane would have saved SEA-HKG, but it might have helped the case a little at least...