The fairy tale-themed Magic: The Gathering set Throne of Eldraine introduced the Showcase Frames, alternate versions of cards in the set featuring different art and a special frame (you can see the Showcase "Order of Midnight" below), but it looks like Wizards of the Coast will continue to print cards with Showcase Frames in future MTG sets including Theros Beyond Death, but don't expect them to have the same storybook look as Throne of Eldraine's Showcase cards.
A German website called giga.de recently interviewed Magic head designer Mark Rosewater about card design, and when he was asked if Showcase Frames will also appear in other Magic sets, Rosewater said, "Showcase frames aren’t just a Throne of Eldraine thing. They’re a new addition to the game that players will find in every Standard-legal set. Note that execution of the showcase cards will vary from set to set. The storybook look is just a Throne of Eldraine thing. The next set (Theros Beyond Death) will have its own unique showcase frames that makes sense for the theme of that set."
Since Theros Beyond Death will feature the underworld of the Greek mythology-inspired plane, the Showcase Frames will probably use death or afterlife as a theme instead of the fairy tale style that Throne of Eldraine featured. I can't wait to see what they the Showcase cards of Theros Beyond Death and other future sets will look like.
If you want to know some of the Theros Beyond Death cards that will probably get a Showcase version, check out the leaked cards from the upcoming set.
Theros Beyond DeathMagic: The Gathering