Since I've completed the subject ORD-SEA flight in F last Sunday, I've decided to report on the result.

The new F dinner service consists of a choice of a salad with chicken slices (I didn't actually see the salad nearby) or a pastrami and cheese on rye sandwich with a scoop of some sort of relish alongside. Desert consisted of a miniature Toblerone candy (about 1/4 size of a regular bar).

According to the comments by Carfield above, this will be the F dinner service on the new Dallas route as well. Actually, I think AS could get away with downsizing further on this new route because:

1. on the Chicago nonstop route AS has to compete with several "high-end" carriers (United and American) as well as differentiating itself from the "low-end" (Southwest) -- but on the Dallas nonstop route the only competition is a single airline (American) and Southwest is prohibited from competing from Dallas-Love Field due to the Wright Amendment.

2. the Dallas-SEA route is actually slightly shorter than Chicago-SEA.

Also, refer to my original post above for details on the new AS F breakfast service on the Chicago route (and apparently Dallas as well).