We don't know what the new food is going to be, since they've haven't rolled it out yet. But based on the description, it sounds better to me than what's served now.
It also sounds like a likely upgrade for coach passengers. These are meals that can be sold in the cafe, where the food on long distance trains is even worse than what's in the diner. Amtrak has an incentive to sell as many boxed meals as possible. The boilerplate about maybe not always being available for all passengers is a disclaimer, not a business plan. They don't want to overstock, but with a little experience (which they might already have, via the Empire Builder) they can make reasonably accurate predictions.
I'm looking forward to seeing the new menu on the Starlight and Zephyr. Although not as much as I'm looking forward to seeing them run on time. I know, a long wait.