The back of Magic: The Gathering cards are iconic. Mimicking, more or less, the leatherbound cover of a spellbook, it has five gemstones inset in the center, and the words "Magic The Gathering" at the top. Mysteriously, there's also the word "Deckmaster" at the bottom. It's very much an artefact of 1990s graphic design, and to those unfamiliar with the game it might even seem outdated. But as any Magic player will tell you, the card backs can't change. Cards from 1998 and 2002 and 2022, and every year in between, are still valid cards, so the card back can't change without giving away information about what you have in your deck.
There's actually a long and fascinating story about the card backs, and it's been told in The Duelist magazine and on lead designer Mark Rosewater's podcast. I'm no expert, but to summarise, "The Gathering" was intended to be the first of many "chapters" of the Magic game. "Deckmaster" was meant to signify a sort of parent brand that would encompass many different games, including Magic, Jyhad, and Netrunner.
But most significantly, the second expansion of Magic: The Gathering was designed, and very nearly printed, with the name "Magic: Arabian Nights" and a purple card back. At the last minute, game designer Skaff Elias lobbied to have the card backs remain consistent across all expansion packs of Magic: The Gathering to ensure that players could build decks containing cards from all different sets. In other words, the initial assumption was that each release of a new Magic expansion would be its own self-contained game, but just before the first expansion was released the decision was made that every Magic card ever printed would have exactly the same card back, to ensure that all cards could be used in all games.
The fear was that changing the backs of each set would prevent people from using cards they'd bought previously. I see the logic in that, and I can imagine making the same decision in their place. But sometimes a thing is only a problem after it's been belaboured, and I think this is a good example.
I feel this puzzle can be solved with a simple exercise:
Obviously you're not going to be able to predict the cards of your hybred deck. But by the early Magic team's logic, any time you come upon a different colour card, you should be able to guess it correctly because it has a different back than some number of cards that came before it.
It's an illustrative exercise, but I think it explains it well enough. Even if there had only been two decks of Magic and then the game had ended, players could have easily mixed brown cards in with purple cards without losing the element of surprise. Sure, the different back would have narrowed the scope, but the exact card would still be unknown to both players.
But by keeping the card backs on every set the same, the makers of Magic are implying that all Magic cards are literally the same game. In reality, of course, there's a ban list that deprecates cards that turn out not to be as compatible with other sets as the designers had hoped. Amazingly, the ban list pales in number to the tens of thousands of cards they've created in the past two decades, so mostly they're technically right. And yet there are nuances to sets, and to set identity.
I think Magic: The Gathering doesn't want to admit it, but the fact is that new card sets are essentially new games. I don't think that's a bad thing, but I do think it's accurate from a player perspective. With each set, hundreds of new cards are generated, new mechanics are added, old ones are left out. Mechanics are omitted from sets based on theme, as when the Dark Ascension team decided to not use negative counters in favour of positive counters to keep with the theme that monsters only get stronger, and Lorwyn decided mechanics based on whether the setting was the light world or the dark world.
Technically, compatibility is retained with previous sets, so you can buy the new "game" but use the cards with your existing collection. In practise, though, each set has internal synergy. This is by intent. Sets are designed so that cards can be drafted from booster packs so that a functional game can be built solely with the cards in that set. They're self-sufficient.
It's true that each expansion has a tiny expansion symbol on the front of the card, but there's already so much data on the front of a card I think it gets overlooked pretty easily. And even when you don't overlook the symbol, they all start to look the same after a while.
Unique card backs would help identify card sets quickly, and reinforce the idea that there's greater synergy within an individual set than in all Magic cards crammed into one big cube.
Unique card backs would also promote viewing each set as a unique game, which actually hearkens back to the original intent of the game anyway.
There would still be formats that combine sets, obviously, but different coloured backs would strengthen Magic's real money makers (Booster Draft and Sealed) while also providing clarity in other formats.
You can, of course, imagine a gamer gaming the system. It's what we gamers do. I know I'd try to.
Build a deck with just my finisher taken from the expansion deck, so I would always be aware of when it's top of deck.
Or maybe I'd just put a few key cards in my deck, so even though I might not know the specific card, I'd know roughly when the "special" cards are coming.
Or I could take all my lands from the expansion so I would at least know when an upcoming card is a spell.
So you develop rules to forbid this behaviour (if you want to forbid it). Maybe you print all land cards with the original back, or maybe you require that when using a unique expansion, at least 4 different card types must be present.
I imagine there are edge cases. Maybe a red expansion set comes out that contains all bad cards, except one card everybody loves. If you put a red card back into your deck, everybody knows which card it is, because it's the only card worth playing from the red expansion.
Or maybe the inclusion of gray cards from that all-artifact expansion would reveal that your deck consists largely of artifacts.
I'm confident that problems would arise from having different card backs, just as problems arise now from having cards that turn out to be over-powered in certain formats, or cards that interact with each other in unexpected ways, or cards that were once powerful but are overshadowed by new ones, and so on. Quirks in a game of 25,000+ cards are to be expected, but they get solved. And sometimes the quirks, frankly, add a lot to the flavour of the game.
With the benefit of hindsight, it's easy to spectulate that the decision to keep a unified card back was probably a vital component of the continued success of Magic: The Gathering. Even though I believe different backs wouldn't have hurt the game, if the perception was that it would hurt the game then people may not have invested as much into MTG for fear of each set becoming deprecated the next year.
So we have one design for the card back today, and presumably we always will have. But it's fun to speculate, and I think I'd prefer a new look for each set.