Star Wars fans had guessed Rey's lightsaber twist in Star Wars: The Rise of Skywalker back in 2014, a year before Star Wars: The Force Awakens had even been released. As a character who more than proved her skills wielding a staff as a scavenger on Jakku, it only made sense that JJ Abrams would pay off this setup at some point during her three-episode tenure.
Throughout the majority of Star Wars: The Force Awakens, Rey's weapon of choice was her salvaged quarterstaff. Her sole source of defense while she lived alone on Jakku, Rey's staff became somewhat emblematic of her character, despite the fact that she eventually opted for Anakin Skywalker's former lightsaber by the end of the film, throughout all of Star Wars: The Last Jedi, and for the majority of Star Wars: The Rise of Skywalker - until the final few minutes when she revealed her brand new lightsaber, made from the hilt of her original staff. Incidentally, some devoted fans had predicted this back in 2014.
While it would have been close to impossible to predict that the color of Rey's lightsaber blade would be yellow (it wouldn't have been an educated guess, but a lucky one), it was only right that Rey's capability with a staff would eventually get a payoff. And it did. Fans and teaser breakdowns from various outlets called attention to the fact that Rey's staff looked like the hilt of a lightsaber, and - roughly five years later - it turns out they were right.
Incidentally, the final design of Rey's lightsaber wasn't finalized until Star Wars: The Rise of Skywalker was being developed. However, it's rumored that Colin Trevorrow's draft for his take on Star Wars 9 included a version of Rey's final lightsaber that was utilized much sooner in the story. The main difference, according to as-yet-confirmed leaked concept art from the film, was that it would have been a double-bladed lightsaber with blue blades. It was reportedly intended to be a hybrid of Luke Skywalker's lightsaber and her staff.
Though some fans may have been disappointed to see the reveal of Rey's final lightsaber saved for the very end of the film, it's still a satisfying payoff. It felt like a missed opportunity to follow Rey's journey in becoming a Jedi without using a tool with which she's already proven to be experienced. That said, even Abrams himself addressed the fact that it'd have impossible to please everyone. The fact that it was paid off at all is satisfying enough.
Source: Den of Geek