The anticipation is sky-high for the mutants' official arrival in the wider MCU, especially after Marvel Studios President Kevin Feige mentioned in 2021 that the reboot for X-Men has been "long and ongoing internally."
In fact, Ms. Marvel's finale already retconned Kamala Khan as a mutant instead of an Inhuman. Ms. Marvel actress Iman Vellani even "freaked out" when she learned about the big X-Men reveal.
Secret Invasion's X-Men Tease Explained
In Secret Invasion Episode 4, a book written by Priscilla Fury named Decoding the Superhuman Gene inside Varra and Nick Fury's home can be seen in the background of Varra's home.
The Superhuman Gene in the book could refer to the X-Gene of the mutants. In Marvel Comics, the X-Gene is what causes mutants to develop superhuman abilities that manifest at puberty.
It appears that the book discusses the X-Gene, hinting that the public is now aware of mutants.
In the Ms. Marvel finale, Matt Lintz's Bruno Carrelli was shocked when he discovered Kamala's genetic anomaly. This meant that the X-Gene implications were not uncovered then.
Given that Secret Invasion is set in the "present-day MCU," it's possible that major facets of the government, including a significant portion of the public, have a general idea that there's a genetic anomaly amiss.
How This Secret Invasion Reveal Leads to X-Men Reboot
It is unknown why Priscilla Fury decided to write a book about the superhuman gene, considering that she's secretly a Skrull. It's possible that Gravik ordered Priscilla to conduct some research about the X-Gene, potentially as their first attempt in their Super Skrulls upgrade/experiment.
There's a chance that the superhuman gene research didn't live up to the expectations of Gravik and the Skrulls. As a result, Priscilla could've used this book as a way to distract the general public about the X-Gene from the impending Skrull threat.
On the flip side, Priscilla may have created the book so that her research about the gene will be documented and not put to waste.
This book about the superhuman gene could lead to massive ramifications across the MCU, potentially leading to a possible conflict between humans and mutants down the line.
In Marvel Comics, there are several anti-mutant groups, such as the Human Council and the Orchis, and this book could give birth to the live-action iterations of the said organizations.
Moreover, the discovery of the X-Gene could also alert the Avengers, prompting the team to address the next steps like researching if mutants are a threat.
Secret Invasion is streaming on Disney+.