I disagree DOFP will have different takes on many characters that people will have to accept. Saying this is the Daughter of Scott and Jean in an alternate Universe is not that confusing if they have a part for her. Thats all you need to know. Look at how they present back stories to Emma Frost, Havok and Banshee. They rarely go in detail on anyone.How does the general audience even know Havok is Cycs brother? They could even mention her name and not even mention whos daughter she is, since the GA probably wont care in the long haul. Her parents would be probably dead anyway whatever universe they are in. If they wanted to use her at all in the film series DOFP is probably her only chance. She makes more sense to me then others. I would also like to see Nathan Summers who you could probably make the same arguments about.
Being logical as you said earlier to figure out a film that we know next to nothing about that uses possible time travel, different timlines and could litterly go any way it wants with introducing new characters in a franchise that seems to already pick its Mutants at random is a lil bit difficult, and is anyones call at this point. Its nothing more then personal preference. Using characters who are from the actual DOFP story, would not be a bad way to start discussing imo.
I agree that if they follow the comics, then they could introduce Rachel.
The DoFP story came in the comics a few issues after the death of Dark Phoenix - and Scott and Jean had not had a daughter in the comics before Jean died.
But it does feel odd to me that Rachel is teavelling back to a time where she could not have been born.
Surely, her time travel would go back along the timestream to a period where she could have been born (ie where Jean didn't die). She seems to have jumped into another timeline altogether.
In other words, the X-Men are asked to stop a future that wouldn't have happened anyway in their timeline because Rachel couldn't have ever existed in the present day of the comics at the time.
In my view, Rachel Summers is problematic for that reason.
Firstly, the Summers connection, as I explained above. She would be better introduced if travelling back from a distant future to a present day of the X2/X3 time period, when Scott/Jean already existed.
To bring her back into a time when Scott and Jean have not yet been introduced is odd.
Also, she has Phoenix-like powers and visuals and the audience will notice that connection to Jean Grey even if you decide not to explain it.
Rachel is obviously from a timeline that is nothing to do with X1/X2/X3 (because Jean/Scott died before having a daughter), so that is immediately introducing another alternate reality altogether.
Let's look at the Star Trek model. It didn't open with the daughter of Kirk and Uhura suddenly appearing from some future where those two had got it together and had a child.
It introduced the older Spock from what we can believe to be the established canon (from previous films and series) and then created an alternate timeline because Spock had changed the past by going through that black hole.
I think the key to not confusing audiences is to accept that X1, X2, X3 and Wolverine are the established canon, and that they led to the dystopian future from which someone travels back (mentally or physically). This means that Jean and Scott didn't have a daughter.
However, they may well choose to introduce Rachel and simply say that the assassination of Kennedy (or whatever the pivotal event is) led to a future in which Scott and Jean had a daughter. For me, it's an issue in that we haven't met Scott and Jean yet in the First Class films.