Before we dive into it, for those that are unfamiliar Destiny:Rising takes place in an alternate universe that is post-Collapse but pre-City Age. While there are numerous pieces of lore/characters/concepts that are similar and fit right in to the main universe, there are tons of differences (for example giant robots fought massive ahamkara).
Now things get interesting when it comes to exotic weapons, there are 8 brand new to the franchise exotics and 12 that Destiny players would be familiar with. Each of the new one’s has a standard piece of flavor text and lore tab, but the returning one’s all have related flavor text, in the format of “Retrieval Record 00xx: xxxth Solar Day — [Location, Location]”. For example, Crimson, is “Retrieval Record 0014: 247th Solar Day — The Last City, South America”.
More interestingly, the lore tabs of the returned exotics all feature stories around “Project Clotho” a project that involves sending Lightbearers to OTHER TIMELINES in order to borrow/steal/recover exotic weapons. While some of these are likely alternate-alternate universe’s (one location is Spider’s grave, the Reef), some of these timelines are heavily implied to be the main Destiny Universe. Crimson being amongst the strongest implications. See the lore tabs for example:
Crimson D2
"This is crazy! You don't need this thing. I can heal you; that's my whole job."
"I thought your job was to state the obvious."
"What?"
"Oh, come on. Ever since you found me, it's been, 'Watch out, Fallen ahead!' when they're right in front of me. Or, my favorite: 'Seems like the door's locked.' Is it? Really? I couldn't tell. And when it's not that, you say I need to be more self-sufficient in case we lose the Light again. So here's my answer. Here's the remedy."
"I was just trying to help."
Meanwhile in Rising
"This is crazy! You don't need this thing. I can heal you; that's my whole job." Hazel expands her shell in an aggressive display, blocking her Lightbearer Samuel's face. He tries circling around her, but she nimbly moves to the other side, blocking him again.
"I thought your job was to state the obvious." Samuel returns the gun to its holster, crossing his arms across his chest as he leans against the door frame. There's an unnamed, wicked fire flaring in his heart. He'd almost won that match. Now, he has to find a way to explain to those bloodthirsty gamblers why their money's been flushed down the drain—unlike at Shaxx's Crucible, those lunatics have no qualms about getting their hands dirty, nor any rules to speak of.
"'What”
"Oh, come on. Ever since you found me, it's been, 'Watch out, Fallen ahead!' when they're right in front of me," Samuel shouts. His mind is elsewhere now, but footsteps cut his complaining short. His heart sinks, and his right hand moves for his holster as a barrage of questions swirl in his head. Those bastards wouldn't be crazy enough to attack right under Shaxx's nose, would they? Who would bear the consequences of starting a fight on Shaxx's turf? Does this break area have any exits aside from the stairs in front of him?
A relatively short woman—unarmed, he notes-then rushes over and stands before him. The first question out of her mouth is, "Samuel, right?"
Samuel tries taking a few steps towards the stairs, attempting to switch positions with the woman. She seemingly has no intention of stopping her.
"Who's asking?" he responds tentatively. She looks aggressive, but not unreasonable.
"I'll keep it short and sweet." She points at Samuel's holster. "Give me that gun of yours, and I'll take care of your problems for you. ALL your problems.”
Or, maybe it’s just an alternate alternate universe that was stepped into, one that’s almost identical to the mainline franchise.
We know Bungie consulted with NetEase regarding a few aspects of the game, lore included. So at the very least, this is likely as close to official confirmation that we’ll get, that the Last City is in South America