We've been waiting what seems like forever to finally get our hands on Kingdom Hearts III. After years and years of waiting and teaser trailers, the game's director finally explained exactly why it's taken so long to get the game made.
There was a decision made to change to an external [engine]...Unreal Engine 4, so we switched over to that. Unfortunately there was a bit of time that needed to be rewinded and started over. So there was a bit of a setback there, but it was a decision that the company had to make, so it was inevitable.
According to the article, it took the team an entire year to make the conversion and then pick back up and continue development after moving over to the Unreal Engine 4 after starting out with Square's own internal engine.
This is about the average time it takes to move over to a whole new game engine. Usually it requires completely reworking the developmental pipeline, which also means completely converting over the assets into the pipeline, updating the code and package structures to the new engine, and then finally optimizing all of it to accommodate the new software.
The Unreal Engine 4 is definitely a highly optimized and very efficient game engine, but it still takes a lot of time and a lot of effort to move over a game from one engine to the next. In the case of Kingdom Hearts III, there was an entire year's worth of content that had already been finished that then needed to be moved over, reworked, or scrapped.
So, keep in mind that after the game was originally teased back in 2013, it sounds like the switch happened in 2014. That set the team behind by a year, which meant that the game actually hasn't been in development quite as long as some may have expected. Three years of development so far is about average, and the game is set to release in 2018, so that would bring the total development time up to around four years, which isn't too out of the norm for a AAA big-budget blockbuster title.
One of the things that Nomura also revealed was that he had requested more personnel as development began ramping up for Kingdom Hearts III. This is typical for most projects as they begin to scale in scope and size. However, Nomura mentioned that the personnel he was provided with were very limited and that Square was quite reserved in how the company issued resources to the different departments.
So that's exactly why it's taking so long for Kingdom Hearts III to release. On the upside, you'll be able to get your hands on the game for the Xbox One and PS4 starting in 2018.