Make the entire cabin one high density seating configuration using the narrow window seats as the template, remove the bar, market it as premium economy, done. That would sell. 

How did the suite and bed width compare with other Delta One Suites on narrower aircraft such as the A350 and A330? Did the extra cabin width of the 777 translate into more spacious suites or was it just allocated to wider aisles?

It will be all about how they configure the cabin. If they configure the A321XLR with 18 inch wide seats, 32 inches of pitch and a modern IFE with wifi then I'll take that over a cramped 9-abreast 787 or 10-abreast 777 anyday.

In general, Airbus cabins in economy are more comfortable than the equivalent Boeing cabins. 9 abreast in an A350 or 8 abreast in an A330 beats 9 abreast in a B787 or 10 abreast in a B777 any day. Yes, there are some exceptions like the 9 abreast AirAsiaX 333 or 10 abreast Air Caraibes 350, but...

That's a good point. However it raises even more questions. At what price point do they charge for the sleeping bunks? Too cheap and it doesn't make economic sense for the airline. Even worse if the price point was relatively low it might cannibalize sales of business class seats. Too expens...