The 'developer comments'-section mentions a startdate of 1471 for the game. It is probably not wrong to assume that with the standard 1-day-per-turn time system the end date will be considerably later than 1592, the year Toyotomi Hideyoshi invaded Korea in what is known today as the Imjin War. This war ended up being a disaster for both Korea and Japan, and ruined the ruling Toyotomi clan - So it cannot be said to have no significance in a Japanese-focused game.
So far there have been no comments confirming or denying the inclusion of this war. Is the dev team considering to 'unlock' the Korean peninsula (with Korea as a non-playable entity) in any game during which a faction unites Japan? The combined Joseon/Ming forces would make an excellent endboss and keep things interesting after having achieved so much (a common problem in paradox games)!
So far there have been no comments confirming or denying the inclusion of this war. Is the dev team considering to 'unlock' the Korean peninsula (with Korea as a non-playable entity) in any game during which a faction unites Japan? The combined Joseon/Ming forces would make an excellent endboss and keep things interesting after having achieved so much (a common problem in paradox games)!