Okay, I know this thread is about a week old, but hear me out.
I think Strelitza is a possible red herring much like how Lauriam himself is a possible red herring for her murderer. However, I think she was deliberately written to be the Nameless Star in case audiences didn't react well to the idea of Yozora and Verum Rex or if SE wouldn't approve of their use because of of whatever reason. I think Strelitzia was always a viable option, but with the release of Re:Mind and knowledge of the characters of both Strelitzia and Stella, we can begin to piece together why this theory has more weight to it than you might have thought.
First things first, context on Nomura's mental state. He is most certainly not fine and he is also not above meta storytelling. And we know that he's still hurting from his dream project being taken from him. In a Dissidia NT livestream focused on Noctis' inclusion into the game, Nomura flat out admitted that he cried as he drew him for the first time in years. Recently, with the release of Noctis' protoype outfit from Versus XIII (which Nomura flat out stated as well that it was never gonna be Noctis' final outfit), Nomura expressed surprise when Kujiroaka and Hazama talked about Versus XIII by name. He asked if they were allowed to talk about it, suggesting that he had been banned from saying anything about the game. That doesn't seem like an environment that would allow him to just get over his feelings on being removed from XV.
And with that, on to the main points. Now, to start off with, it was actually a slight mistranslation on what Nomura had said regarding the Nameless Star. It is said that he said she was a character who had already appeared in the game that we knew, but he didn't give specifics. So, he didn't say it was character either we the player or Sora had already seen play a role within the series. He is just saying we have seen the character before and as one person mentioned before me, that doesn't leave out Not!Stella.
Now Strelitzia seems like the only logical choice concerning The Nameless Star. I mean, she's dead and her place was taken by somebody so they could infiltrate the Dandelions and Lauriam is searching for her. And he was subjugated by Xehanort as Marluxia. That does fit... until you look at how Strelitzia and the Nameless Star talk. UX, Strelitiizia is shy... very very shy, to the point where she is also rather fretful and anxious, qualities we do not see the Nameless Star possess. Now, you could say its because she has had some time to adjust, but at the same time, it seems odd that Strelitzia would speak so calmly and matter of factly about both her death and talking to a complete stranger. Many people have pointed this out, but Strelitzia just doesn't sound quite as confident as the Nameless Star does when speaking to Sora.
Now, for Stella, the parallels are actually more consistent. And I know what you are going to say, that we didn't know anything about Stella, but putting aside that that's nonsense just in general, we do have a video of Noctis and Stella that you might have come across before, as it was the very first ingame representation of both them and the world they inhabited.
Now, first and foremost, this is a prototype of the scene, this was changed both in the official gameplay trailer and was set to be an FMV in the final game. But the one thing that hasn't changed is Stella's personality throughout all this. She's confident, she's proper and well spoken and she has no problems with talking to a complete stranger, especially one whom she knows is a prince. Even then, she even offers to invite Noctis to her city and offers to show him around. These are all things that Strelitzia lacks but the Nameless Star does show signs of.
Then there's motifs. Strelitzia's motif are flowers, not stars. The particular genus of flower is not related to stars in symbolism either. Aside from the obvious mention of Stella's name and jewelry being being star related, she's shown with only one other character in a cutscene that also shares this motif, though in a much smaller way. Yes, I'm talking about Namine. Remember that Namine had a mild star theme in CoM, from her "good luck charm" to the shooting stars in her "backstory". She is also noted to look like a younger version of Stella, as she has blond hair and a white dress. While Not!Stella is red headed instead of blond, the star theme and white dress are heavily apparent in her design.
And this one is to be taken with a grain of salt, but the Japanese fan base 'found out' that Stella and The Nameless Star share the same Japanese voice actress. A comparison can be found in this little known video, though I'm still myself iffy on if this is true. I only include it for completions sake.
However, if this is true, then it fits in with how Yozora appears to be voiced by both Tatsuhisa Suzuki and Ray Chase like Noctis is. Now again, take it with a grain of salt, as we do not know if they are indeed voicing Noctis, but as Ray Chase is involved with franchise as the Master of Masters and Nomura implied that him and Yozora share a connection. And Yozora has been seen in a night version of the Final World, meaning that he possesses the ability to go there much like Sora does.
And yes, I do believe she will be called Hoshi if this is true, but at this time I will not call her that and just refer to her as Not!Stella until a name as been given. Regardless of if she's the Nameless Star, she's still gonna show up like Yozora has.
EDIT: A minor edit, but I did want to say that it was more that Nomura implied a connection between Yozora and MoM than actually confirm it. As one person has pointed out, he never actually did, at least not that I can find. It was a slight oversight when I initially pointed it out. Everything else I've said is exactly as I wanted to say, however.