As with the Pathfinder games, developers Owlcat plan to document the creation of Warhammer 40,000: Rogue Trader with a series of dev diary videos on its YouTube channel. The first of them features lead narrative designer Olga Kellner giving an early look at the spacefaring CRPG.
Kellner says players will get to enjoy "space exploration, voidship battles, intrigues, weird warp phenomena, and many other things" recognizable from the Warhammer 40,000 setting. As a voidship captain with an unusual degree of freedom on the fringe of the Imperium, including control of a merchant empire, players will get to make decisions with consequences reflected by the setting and its characters. We might, for instance, "stay faithful to the Emperor or test the limits of your privileges and the Inquisition's patience, wreak havoc on your planets, consort with the enemies of humankind, even fall into the clutches of Chaos."
The dev diary also has a look at our entourage, with recruitable companions including a seneschal, a psyker, a Sister of Battle, an eldar ranger, a tech-priest, and a space marine of the Space Wolves chapter. Owlcat's website has already documented a couple of these characters, so we know the seneschal is a man of duty named Abelard Werserian, while the psyker is a diviner named Idira Tlass, "a tortured and broken soul haunted by the whispers from beyond the veil."
Owlcat's website also introduces Lord Captain Theodora von Valancius Massimo af Scarus, the head of a dynastic family of rogue traders who "owns a voidship crewed by thousands of loyal servants, reigns over a vast conglomerate of worlds that bring her immense wealth, and vies for supremacy with the other Rogue Traders of the Koronus Expanse". Seems likely she'll be our character's mentor, and maybe we'll inherit her voidship.
Unlike Owlcat's Pathfinder games, Warhammer 40,000: Rogue Trader will only have turn-based combat. It's inspired by a tabletop RPG of the same name published by Fantasy Flight, though "it won't be a direct transfer from tabletop to a videogame" according to Owlcat's community manager on Reddit.
Though there's no release date yet, the preorder FAQ says an alpha of Warhammer 40,000: Rogue Trader is planned for this year, with a beta following next year.