Today Sega confirmed that Valkyria Chronicles 4 is coming to PlayStation 4 in 2018, complete with a Teaser Site including a PS4 Announcement trailer video and details below! 
From the video's caption, to quote: The continent of Europa is engulfed in the flames of the Second Europan War between the Atlantic Federation and the Autocratic Eastern Imperial Alliance.
Although the Federation struggles valiantly against the Empire’s forces, the relentless imperial military machine threatens to consume them.
With victory slipping away, the Federation executes Operation Northern Cross: a last-ditch attempt to capture the imperial capital and end the war.
Commander Claude Wallace and his loyal childhood friends in Squad E are sent to fight for the desperate operation’s success, but they will have to endure harsh bone-chilling elements, waves of imperial soldiers, and the terrifying Valkyria... and unravel a grave truth that will shake them to the core.
Here's some additional details from Sega's PR Associate Will Chan as well, to quote:
When did Valkyria Chronicles 4 begin development?
Kei Mikami: It’s been about two years since the project officially started. It might be a little longer if you include the time our director, Mr. Yamashita, spent in the planning phase.
What brought you back to the world of Valkyria Chronicles 4?
Kei Mikami: The aim of this Valkyria Project is to expand the series on a global scale. We haven’t released a mainline title since Valkyria Chronicles 3 in 2011, so our goal from the beginning was to attract new audiences worldwide. Our overarching vision is to return to the original Valkyria Chronicles’ roots, while building on improvements from the rest of the series. Valkyria Chronicles 4 is the culmination of everything we’ve learned up to this point.
We began setting the groundwork for this project with Valkyria Chronicles Remastered for PS4. Our intent was to let fans experience Valkyria Chronicles’ origins and core gameplay on a next-gen console before moving forward with a brand-new numbered entry to the main series.
What inspired the story, characters, and setting?
Kei Mikami: Valkyria Chronicles 2 and 3 were both released exclusively on PSP, which was a very prolific console in Japan. Their themes, therefore, catered to our Japanese audience, such as a schoolyard environment or a fantastical special ops team. This time we decided to return to the first game’s grounded military setting. As such, we moved away from super soldiers with extraordinary powers. Instead you’ll find characters who are more like people you could see yourself meeting in everyday life.
We gathered reference material by studying countless records of the troops who participated in World War II. In doing so, we learned about soldiers who never lost hope, even in dire straits. Perhaps it was their youthfulness that allowed them to hold onto that positivity. These tales of soldiers whose dreams were crushed by the stark realities of war, only for them to stand back up and face that reality head-on, affected our team on a deeply emotional level.
What makes Valkyria Chronicles 4 different than the rest of the mainline series?
Kei Mikami: The first Valkyria Chronicles games focused on the small country of Gallia. This time around, the world itself is expanding to reveal an epic story that covers the full scope of the Second Europan War. We recreated a world history loosely based on the frontlines of the Eastern Theatre and want you to experience a different side of the Europan conflict. How did the war impact other continents? What lies beyond the Gallian front? Discover the global impact of EWII through the mechanical improvements and narrative innovations of our latest creation.
What’s new about the Canvas system?
Kei Mikami: New hardware allowed us to repaint the gorgeous visuals you know and love in a whole new light. In order to amplify Canvas’ hand-drawn, watercolor aesthetic, we deepened the shadows to make its colors pop. We also added real-time environmental effects — like footprints left in the snow, or heatwaves warping the air around you — to give the sense that you’re actually there in person.
From the video's caption, to quote: The continent of Europa is engulfed in the flames of the Second Europan War between the Atlantic Federation and the Autocratic Eastern Imperial Alliance.
Although the Federation struggles valiantly against the Empire’s forces, the relentless imperial military machine threatens to consume them.
With victory slipping away, the Federation executes Operation Northern Cross: a last-ditch attempt to capture the imperial capital and end the war.
Commander Claude Wallace and his loyal childhood friends in Squad E are sent to fight for the desperate operation’s success, but they will have to endure harsh bone-chilling elements, waves of imperial soldiers, and the terrifying Valkyria... and unravel a grave truth that will shake them to the core.
Here's some additional details from Sega's PR Associate Will Chan as well, to quote:
When did Valkyria Chronicles 4 begin development?
Kei Mikami: It’s been about two years since the project officially started. It might be a little longer if you include the time our director, Mr. Yamashita, spent in the planning phase.
What brought you back to the world of Valkyria Chronicles 4?
Kei Mikami: The aim of this Valkyria Project is to expand the series on a global scale. We haven’t released a mainline title since Valkyria Chronicles 3 in 2011, so our goal from the beginning was to attract new audiences worldwide. Our overarching vision is to return to the original Valkyria Chronicles’ roots, while building on improvements from the rest of the series. Valkyria Chronicles 4 is the culmination of everything we’ve learned up to this point.
We began setting the groundwork for this project with Valkyria Chronicles Remastered for PS4. Our intent was to let fans experience Valkyria Chronicles’ origins and core gameplay on a next-gen console before moving forward with a brand-new numbered entry to the main series.
What inspired the story, characters, and setting?
Kei Mikami: Valkyria Chronicles 2 and 3 were both released exclusively on PSP, which was a very prolific console in Japan. Their themes, therefore, catered to our Japanese audience, such as a schoolyard environment or a fantastical special ops team. This time we decided to return to the first game’s grounded military setting. As such, we moved away from super soldiers with extraordinary powers. Instead you’ll find characters who are more like people you could see yourself meeting in everyday life.
We gathered reference material by studying countless records of the troops who participated in World War II. In doing so, we learned about soldiers who never lost hope, even in dire straits. Perhaps it was their youthfulness that allowed them to hold onto that positivity. These tales of soldiers whose dreams were crushed by the stark realities of war, only for them to stand back up and face that reality head-on, affected our team on a deeply emotional level.
What makes Valkyria Chronicles 4 different than the rest of the mainline series?
Kei Mikami: The first Valkyria Chronicles games focused on the small country of Gallia. This time around, the world itself is expanding to reveal an epic story that covers the full scope of the Second Europan War. We recreated a world history loosely based on the frontlines of the Eastern Theatre and want you to experience a different side of the Europan conflict. How did the war impact other continents? What lies beyond the Gallian front? Discover the global impact of EWII through the mechanical improvements and narrative innovations of our latest creation.
What’s new about the Canvas system?
Kei Mikami: New hardware allowed us to repaint the gorgeous visuals you know and love in a whole new light. In order to amplify Canvas’ hand-drawn, watercolor aesthetic, we deepened the shadows to make its colors pop. We also added real-time environmental effects — like footprints left in the snow, or heatwaves warping the air around you — to give the sense that you’re actually there in person.
