The design predecessor for the corridor bi-levels is the Surfliner, not the Superliner. The Nippon-Sharyo cars will have 2 doors on each side and I expect numerous internal changes from a Superliner II design. Amtrak can use the coach and BC-cafe car designs with different seating for LD coach cars. But sleeper, diner, sightseer lounge, and dorm cars would require a lot of design work and changes from what Nippon-Sharyo is building. N-S would have an advantage in that they will have a new production facility tooled to build bi-level cars that have a lot in common with Superliners, but building sleeper cars or diners will not be a small or modest design and manufacturing change.I agree. If it's a small order it might be able to be "tacked on" as an option to this order.
But even if Amtrak put the Superliner III out to bid Nippon-Sharyo would have a big advantage. Remember the Superliner was used as the design baseline for these cars... so it shouldn't require much retooling to convert the factory from a intercity car assembly line to a Superliner III assembly line.
Since funding to build replacement Superliners will be mostly government money, in one form or another, Amtrak will put out any RFP for Superliner or Amfleet replacements as an open bid. Period.