As part of Sega's End of Fiscal Year 2018 report, the Japanese developer/publisher noted that their "completely new" Sakura Wars title will be released at some point in Fiscal Year 2018, so by definition that means before March 31, 2019.
The game was first revealed last month at Sega's Fes event, which was held in Akihabra, Tokyo. There is very little known about the new entry to the long-running franchise, other than Shin Sakura Teisen is set one year after the events of PS2/Wii entry Sakura Wars: So Long, My Love.
Although the wait for info is quite frustrating for fans (a platform? anything?) they can at least take comfort that, if the game is indeed to be released within the next 11 months, that Sega are going to have to start showing its hand on the mysterious title soon.
Shin Sakura Teisen is currently in development at Sega.