Rising Tide DLC's release date is April 18th, while the Final Fantasy XVI x XIV crossover event is simply in early April and the XVI x Brave Exvius event will also be in April.
Apparently we're getting a new mode called Kairos Gates, which is a 20 stage Survival mode essentially where you can post your scores on a leaderboard, wherein if it's played on Final Fantasy difficulty and you make it through with all S ranks...you unlock a new stage with an "Insane boss character". They refused to elaborate any further than to say that this boss should look good for people streaming the game.
Wonder who the super boss is going to be? Probably someone from Final Fantasy XIV if I had to guess, assuming that it's not just Gilgamesh which I suppose it could be (though he was literally JUST in FFVII Rebirth so maybe not)?