The negative space is quirky but it's not necessarily a bad feature.
I think there's a few things to consider with this design. The Aces of Spades list a name for each deck - Metropolis for the 1920s and Dusters for the 1930s. Why doesn't the name appear on the box? It feels like buying a pack of Mohawk, Caravan or Torpedoes and finding Aviators inside. (USPC used those names for cheap, generic decks at one time in not-too-distant history. As they got out of the generic deck business for the most part, probably as part of the effort to make Bicycle and Bee the two most popular decks in the country, they started using Aviators in the leftover boxes rather than throwing them away, probably because they were the cheapest cards available at the time. I imagine if they made them today, they'd contain either Streamlines or Mavericks.) The boxes also look just too much like each other - there are better ways to indicate the decks are part of a series without sapping away all the uniqueness between the two tuck boxes.
This change in the decks, just that one Ace of Spades card, means he'll be paying for two print runs. You can try to finagle and negotiate with USPC if all you're changing is a back color, allowing the use of the same plates, but in this case the faces plate would need to be swapped out, incurring an extra step - and every step from idea to deck costs money. Which makes me wonder all the more if he's budgeted this project correctly. He hasn't stated that there's any private funding in the project.
Most of the historical decks I've seen cover a specific historical event - World War II, the Civil War, Dia de los Muertos, Christmas, the Year of the (insert Chinese-calendar animal name here), etc. The most notable exception I've seen were the music trivia decks that USPC produced, a series of four decks each covering a decade in modern music from the 1950s through the 1980s. They did reasonably well in no small part due to the number of people still alive who were born at the right time to appreciate the music in each respective decade. With this deck series, he opted to choose two decades in which few people alive today would have lived - for the Dusters, people between the ages of 83 and 74 would have been born then and this doesn't even account for the people who were already alive when the decade began. For Metropolis, it's even worse - people born in that decade would be between 93 and 84 today, older still if they were alive before the decade started. There's less for an audience to identify with than if he'd chosen more recent decades first. Plus using the same card back is kind of a cop-out when you consider the changes in art and architecture that took place in each decade. Realistically speaking, these decks would look better if the buildings on the card backs were of the specific period - a change of construction as well as a change of color.
But most of that would imply that this is meant to be a continuing series - something the creator has given no indication is the case.