Respectfully, you actually bring up a few of the fallacies that lead to this in the first place. Please don't take me pointing these out as me making fun of you, it's just to help you understand, and absolutely not to insult.
When you say that it's easily the easiest interpretation of that line, you're using that conjecture to support a different conjecture. And that's, in a nutshell, how misinformation spreads. I'm going to give you an example and hope I don't ramble on too much, but it's a relatively complex concept that's difficult to explain.
Imagine, for a minute, a public figure wrongfully accused of something. Let's, for the sake of argument, say it's a prominent football player accused of underinflating footballs. Totally random example! lol. And this player, during his press conference looks all nervous. So, the public at large sees this nervousness as confirmation of guilt. And you have two bits of information: A person is accused of a crime, and a person, when speaking about the crime is acting nervous.
So, what's the easiest thing you can attribute that nervousness to? Guilt, of course. So, now you have these two vague points supporting each other in this conclusion. The case I'm obviously referring to was far more complicated than this, but keeping it simple for the sake of discussion. The problem with this is that the two bits of information support each other, without anything tangible to anchor them. Like, in this case, the fact that the science proves that the balls were never actually deflated in the first place.
I'd say a lot of the people are completely unaware they are doing this, so it's not an insult to anyone's intelligence, but when you explain to someone that the speculation about the football deflation is irrelevant because the science tells us there was no crime in the first place, and the response is always akin to "well, then why was he so nervous during the press conference??", that's called post-facto justification and it's the main ingredient in witch hunts.
This may sound unrelated to this game, but it's really not. In a nutshell, this is what's gone on here for a long time. You did it just now by introducing your interpretation of the "My heart won't let go" line as evidence that that's what it refers to. It's self-reinforced in your mind because it seems to fit the other conjecture. The bottom line here is that "My heart won't let go" is as ambiguous as someone being nervous at a press conference.
I've studied this sort of thing for years. It has always fascinated me. And you can spot the signs easily once you get a good grasp of it. Clear as day. In my opinion, the same ingredients that make up a witch hunt are in play. And this is indistinguishable from scapegoating as well. Both are happening to Tabata and it's incredible grating to read it over and over again.
Now, sorry for rambling there, but to your point about them meeting as children or not, that meeting is presented as them meeting for the first time. It's actually a fundamental ingredient to the original premise. The idea that they could have met as kids when the original premise was completely different is a great example of a post-facto justification.
Imagine it's some time before the 2013 E3 trailer was revealed and all anyone knows is what's gone on with the original Stella trailers (including that they have just met for the first time, as evidenced here -
http://web.archive.org/web/20100316...nal-fantasy-versus-xiii-nomura-interview.html - "Famitsu: Can you explain what is happening in the scene from the images released?"
"Nomura: The scene takes place at a party.
This is the first time they have met each other.") . If you were to float the possibility that they had actually met as kids after it was explicitly stated that the premise is that they have met for the first time, you would be run off the board. The justification ONLY makes sense if you look back on it from today and connect the new dot to the old dot. Conjecture in general isn't a bad thing, BTW, just when it's being used as an argument or justification. It's like adding two variables without a constant.
Having "Stella" and Noctis meet as children is already a major departure from the original premise. But more than that, it PERFECTLY fits what is currently the Luna character as it is today. Through and through. That is as close to proof as you are going to get that the female character in the E3 2013 Trailer MUST be Luna in all but name.