Except those rumors were just well, rumors. This was never the vision Nomura had. All along, Stella was put into the same role as Luna EXCEPT on the very first trailers, when there was no plot AT ALL (and are the ones that feature a fighting Stella). The only parts that changed vastly were the pacing and the invasion of Insomnia (in fact, this was where Tabata and co hit a snag. They wouldn't be able to deliver by the end of 2016 if they tried to keep it in.
People need to stop this "Tabata ruined Nomura's game" because there was no such thing as "Nomura's game". It was just a collection of trailers and concepts similar to Agni (which I hope is the project they are working on at Luminous Studio, since they mentioned a new AAA IP). There was no actual plot beyond "Noct and Stella are Romeo and Juliet and fight a so called dictatorship" until you realize there was no plot in between. Admittedly, the concept would've been better than a relapse back into "turning Eos into Remnant II" but hey, at least we got a bloody game and not a load of warm air.
It was far more than just trailers and tech demos. According to reliable sources Nomura had finished writing the story by 2010 and the game was supposedly 25% finished and planned for release on PS3 in 2014 as of the 2011 trailer, but shortly after that Square was shown an early PS4 demonstration, and Square's CEO Yoichi Wada made the decision to transfer it to next gen and turn it into FF15. After that, Square wanted it done as fast as possible, so Tabata and his team were brought in to help with Tabata co-directing. There are reports of Tabata and his team clashing with Nomura and his team, so eventually Nomura was dropped entirely so he could work on KH3 and FF7 Remake, which had both entered early development by that point (December 2013).