In an interview with Gematsu, the game's director Tetsuya Nomura revealed that the game has to be episodic otherwise content would've had to be cut from the final game. Explaining the decision he said:
If we dedicated our time to a single release, parts of it would become summarized. We'd have to cut some parts, and additional parts would come in few, so rather than remake the game as a full volume, we decided to do multiple parts.
Producer Yoshinori Kitase added:
As you can see in the trailer, we showed Sector 1 and Sector 8, but in those areas alone, I think you can see a lot of density. When you're remaking the entirety of the original version in that quality, it's not possible to fit it all in one release.
I am beginning to wonder just how big each of these episodes will be now. Are we talking 20 hours each? 10? 2? I see a play in this where each episode could actually be the size of a standard game, coming together to make a whole package in the end. We will have to wait until we find out more…