The sequel to a Nintendo tactical role-playing game is currently in development for the Switch 2, suggesting that it may be a brand new entry in the Fire Emblem series.
According to the LinkedIn profile of 3D character modeler Taksehi Maruyama, he worked on t

Maruyama’s prior experience indicates that his area of expertise is in the ‘anime’ style of aesthetic, which further points towards a new Fire Emblem game. Nintendo did release a Pokemon-based tactical role-playing game, Pokemon Conquest, back in 2012, but this unannounced title is highly unlikely to be its sequel. There’s also Mario + Rabbids, which is a collaborative effort between Ubisoft and the console maker, hence that can also be ruled out.
It’s worth noting that the 3D character modeler is based in Tokyo while Fire Emblem developer Intelligent systems is based in Kyoto. However, given that he worked on the project in contractual capacity, he likely worked remotely rather than on-site.
The most recent entry in the Fire Emblem series, Fire Emblem Engage, was released on January 20, 2023, for the Nintendo Switch. It sold more than 1.6 million copies worldwide within its first three months on the market. The game’s story focuses on Alear, a divine dragon who awakens after a millennium of slumber and is soon drawn into a war against the dark forces of the Fell Dragon Sombron. Throughout their journey across the continent of Elyos, Alear assembles a team of allies and battles enemies from the hostile Kingdom of Elusia as well as Sombron’s reanimated army. Players control Alear’s forces in grid-based combat typical of the series.