In an interview with Famitsu Weekly magazine, Tetsuya Nomura, the director of the Kingdom Hearts series, has confirmed the reason behind Kingdom Hearts HD 2.8 Final Chapter Prologue is that Kingdom Hearts III is even further away than fans would hope. He also confirmed that the title is being made simultaneously with Kingdom Hearts III. This suggests that the development of Kingdom Hearts III, which has been in development since 2010, may be affected in some capacity.
Nomura also confirmed Kingdom Hearts 0.2 Birth by Sleep – A Fragmentary Passage – will use Kingdom Hearts III's technology and will only last the duration of one Disney world. It is set straight after the secret movie in Kingdom Hearts Birth by Sleep Final Mix. They plan on using using gameplay elements from Kingdom Hearts III.
The cinematic title in Kingdom Hearts HD 2.8 Final Chapter Prologue, Kingdom Hearts χ Back Cover will also show off Kingdom Hearts III's technology according to Gematsu.
When asked for a time frame regarding the release of Kingdom Hearts HD 2.8, Nomura said they cannot announce a certain time frame due to it being developed with Kingdom Hearts III.