There is only one of those...
...and that's the American View, an inspection car rebuilt from a pre-production prototype V1 sleeper stored at Beech Grove. You might as well advocate for dedicated tooling for a Beech Grove or Corridor Clipper. Personally, I think a better use of tooling dollars for a single car type would be for Amfleet II (the long-distance cars with large windows and entrance doors at one end only). Even then, it's an easier sell as an add-on set than a full 4-5 car package.
Unless it's cheaper to bang out all the Viewliner II tooling in one shot (sleeper/diner/baggage/dorm) the two-car add-ons are still an easier sell IMO since you have an established base of Amfleet set owners (of which there are at least 3-4 production runs worth) to sell a couple of extra cars to. And even if significant numbers want to make solid Viewliner fantasy consists, they still can buy both add-on configurations.
---PCJ