No, it doesn't seem like this in any way. Why do so many people believe this?
First and foremost changing a name doesn't make any sense. We finally know that her real name is Lunafreya Nox Fleuret which means that "Luna" definitely isn't an alias for Stella ( what many people thought since TGS). They look different ( Stella seems older) and both have different andornments. Both have similar meanings to their names: Stella ~ Star, Luna ~ Moon which fits perfectly for siblings. But the most important part -> We haven't seen her taking over any scene of Stella from the versus XIII trailers and as long as this don't happen ( and it won't happen) they're most definitely sisters and Stella is the older one.
Fun fact: Back in 2013 Nomura said that finding a voice for Stella was really hard. They needed several years to find a fitting voice actor for her and the result can be heard in the E3 2013 trailer.
There are a lot of people that have opinions on XV's storyline that I don't see how they think either... With Stella and Luna it's something that's purposefully shrouded in mystery. If it was a simple as a rename, they wouldn't have dragged it on this long. What sort of reveal is
LUNA IS STELLA! Pretty underwhelming if you ask me... and not worth the delay in information. So, I think there's still more to it like you say.
Can someone post a picture of the Moogle doll?
Also are the rumors of the Tonberry in the cave at night true?
Look in Cindey's truck hanging by the mirror.
As for the Tonberry... probably not, but I wouldn't know where to look. The Behemoth thing is a lie as well... I killed 15 Behemoths and NOTHING happened... I asked the guy from GameSpot that said this TWICE on Twitter and he hasn't responded to me.