Of course she could still be bicurious (with the tendency to women then as it seems) but what is in Left Behind is definitely one true and stated part about her. For the whole bicurious thing I may refer to her (SPOILER)looking at a men magazine and saying she wants to see what is so great about it.
So basically you say no matter what creators say it doesn't matter. And that makes stories in general useless as they are written with an intention and if that intention is ignored it is not the true story.
It means everything if he says he planned it, no matter if that was from that point on or before. They have the rights, they decide. And he said, they didn't want it to be to obvious but also not top subtle so the kiss alone as well as the comment about "an idea" might technically not be unequivocal but everything together is. He wanted it to be like that and that says everything.
That has nothing to do with believing and one day you will have to accept it. My legal and intellectual property is bound to my rules and no matter if others like it, they cannot decide about it. That counts for every person who owns something, no matter if intellectual or not. Also, as much as others do, you only chose to read what you wanted because my posts even included her to probably not have been a lesbian at first. Another proof you just read what you want is that you were going for hints when I told you he even said he had no intention for it to be absolutely obvious or subtle. That still does not change the fact that it is their brand and they can write and retcon what they want. Retconning will make her a lesbian at that time though as well. They own the brand, they own the right. And what they say about the world is true. You simply didn't want her to be a lesbian which is why you started the argument in the first place. If I had said "I just thought she is" you would have said "she isn't" and now with me using a creator comment you still cannot accept it.
You are struggling against axiomatic things. Creators don't have just "personal opinions" about their game and cannot do anything about it but only thinking as if it is a possibility just as fans can; it is exactly the opposite. If they decide it to be, it is. Just as Albus Dumbledore was declared to be gay and so he is or was until he died. Create something and then let someone complain about you stating something or retconning something of your own work. It does not matter what the others say. You have the right to do so and what you say is more than just an opinion if you make it that way and Left Behind made it as canonical as possible. Neil does not "leave it open to interpretation". He wanted it. It is. And if Ellie later gets attracted to men even though she is interested in girls, she gets attracted to men. Or if they want to retcon something they can do. It is that simple. They decide, not we. And I don't hope anything because I have no problem with her liking girls. And that goes for the whole company as the whole company owns the brand. If some of those who really have a say decide, they absolutely can do so no matter if it is about the ending or Ellie's sexuality.