Figure 1. The first sketch of the smaller 797-6X with 224 seats. Source: JonOstrower.com
The projected 797 would have competitive Cash Operating Costs compared with a modern Single Aisle aircraft like the Airbus A321LR.
The challenge is the capital costs. The A320/A321 and Boeing's 737 MAX models are produced in numbers passing 10,000. An NMA would be successful if produced in 1,000 units. This leads to higher production costs for the numerically smaller series.
The focus from Boeing is therefore on lowering Production costs and on finding Services revenue which can help the 797 business case.