Speaking with Newsweek, Yasue was asked specifically what caused Kingdom Hearts 3’s lengthy development (it was originally announced in 2013):
It was no secret that in 2014 Square Enix made the decision to switch Kingdom Hearts 3’s engine to Unreal Engine 4, a change from the assumed in-house Luminous Studio engine. At the time, Nomura claimed that the change wouldn’t hinder Kingdom Hearts 3’s development, but some didn’t buy the explanation.
Nomura has said in the past that Kingdom Hearts 3 was announced much too early and Yasue’s latest comments support his co-director’s feeling. Considering the game was announced shortly after it started development and then had to go through a complete engine rework shortly thereafter, the evidence is all but undeniable.
Changing Kingdom Hearts 3’s engine multiple years into development, especially with huge new gameplay systems planned, was always going to make the game’s development last much longer. But given the end result, it was likely the right decision to make. Kingdom Hearts fans only need look at the sequel’s trailers to see how impressive the visuals are and how much the gameplay has changed since Kingdom Hearts 1 and 2. Moreover, Nomura and Yasue are clearly happy with the result.
Kingdom Hearts 3 releases January 25 for the PS4 and Xbox One.
Source: Newsweek