To be specific, just the term is trademarked, not the art style itself.
When Octopath Traveler launched on Nintendo Switch last year, one reason it attracted so much attention (which went on to translate into mainstream success for it) was its unique art style. Said art style was a gorgeous modern renditioning of how classic 16- and 32-bit JRPGs used to look, utilizing modern effects and technologies to replicate the look of a sprite based game.
Square Enix used the term “HD-2D” to describe the art, and apparently, they may not be done with it. That’s because Square Enix has filed a trademark in Europe for “HD-2D” and “HD2D”, which seems to indicate that this is a term they plan to use in their marketing going forward. That, in turn, implies one of two things (if not both): that Octopath Traveler is going to become a mainstay franchise, and they will emphasize its artstyle more heavily, or that this artstyle will be used to push more new games from the publisher.
Personally, I would love for Square to use this artstyle to give us remakes of the SNES Final Fantasy games. Can you imagine Final Fantasy IV or VI in this style? That would be amazing. I know the developers of Octopath said they have no interest in doing that, but maybe someone else could be handed the reins of such a project?
Whatever comes in this new HD-2D artstyle, I am sure we will all be interested to see how it turns out. Octopath Traveler is out now, exclusively on the Nintendo Switch.