We know something dosen't feel quite right when Aerith tells Cloud not to fall in love with her. I suspect that Aerith and Sephiroth have some knowledge of what was to come, however there is no certainty of those event occurring in the same way.
I actually didn't have an issue with the changes and expansion to the story. After a while I actually think the ending was really good. I'm also confident that the next game with be even better because Kiatse has said the events will continue as normal. So I don't have a problem with the whispers or circumventing the will of fate at the end of the game. Those things were fine, partly because those things won't change the overall story of Sephiroth, Jenova, the Black Materia, etc.
The issue I have with the ending is Zack and whether he survived. It looks like they are using time travel or multiple realities to undo Zack's death and undo the meaning of life and death to this story. I think we have all heard how bad Kingdom Hearts is and also how the FF13 trilogy is riddled with poor writing with regards to time travel and time related story elements. Those are not things that feel like they belong in FF7 and those things are very difficult to do well even in something like Star Trek which is where they work best.
Time will tell where the story leads next, but if they wreck the story of FF7 with time travel horse manure, it will not be forgiven.
Based on what Kitase said I think the core elements of the original will still remain, but they got to realise that whilst the changes they make now are fairly minor, they're going to add up to some pretty major changes to the journey later down the line. A bit like the GoT TV show versus the books. Even when they still had the original source material, they started making some minor changes that eventually added up to completely different plot arcs by seasons 4/5. That's why I think the ending to this is almost entirely symbolic as a way to prepare fans of the original for a very different journey, even if core aspects are still the same.
As for Zack, my understanding is it was an alternate timeline and probably won't have any bearing on the future of this one. The reasoning being the picture of Stamp in that segment is different to the Stamp that was tagged throughout the game. I can think of a few reasons they might do this:
- To give Aerith some closure on her history with Zack (she seems to be the character that is aware of Zack and Cloud in the ending)
- As an example of how anything is possible in the future (as an addition to the ending text)
- Lay the groundwork for the possibility of a Crisis Core remake/Zack DLC with the possibility of making Zack survive the ending
I don't see them playing too much with Zack and time travel in future parts of the remake as his death is just too pivotal to Cloud's personality and character.