Warning: mild spoilers for The Mummy are ahead!
Even though 2017's The Mummy is a fresh take on the monster that first took Hollywood by storm in the 1930s, there are brief nods to the Mummy movies that preceded it. They were fun callbacks, but for those wondering if there were ever any plans to bring in Brendan Fraser, who played main protagonist Rick O'Connell in the last Hollywood Mummy series, for a cameo or minor appearance, that was never on the table. That's mainly because the large gap of time between The Mummy trilogy and this reboot would have made that problematic. As director Alex Kurtzman explained:
Rick O'Connell was last seen in 2008's The Mummy: Tomb of the Dragon Emperor, which was set in 1946. So unless Rick found some spooky magic to extended his lifespan well into the 21st century, as Alex Kurtzman told ET Online, including the swashbuckling hero wouldn't have made any sense because he's been long dead. And if Rick been turned into a monster, the reboot would have had to spend a significant amount of time explaining to fans of the previous trilogy why he was there, hence detracting from the primary story.
So it's probably for the best that the Book of Amun-Ra (which was used to defeat Imhotep in the 1999 Mummy movie) was the only Easter Egg from that era of Mummy history included in the first Dark Universe installment. But if you prefer thinking that Rick is somehow still alive, imagine that he's been imprisoned by Prodigium because of his monstrous nature, and The Mummy 2 (as in a sequel to the latest movie) would see either Nick Morton or a different protagonist breaking him out.
Even without a Brendan Fraser cameo, including the Book of Amun-Ra in The Mummy reboot served not just as a fun tie-in to the previous Mummy franchise, but also seemed to directly connect both series together. Kurtzman also confirmed to CinemaBlend's own Eric Eisenberg and Conner Schwerdtfeger that The Mummy reboot is in continuity with the Boris Karloff-led 1932 movie. So if one were to assume that the Book's inclusion is more than just a simple Easter Egg, that would mean that all of Hollywood's Mummy movies exist in the same continuity. In other words, Earth has been plagued by a lot of undead, bandage-loving monsters in this world.
The Mummy is now playing in theaters, and Bride of Frankenstein, the next installment in the Dark Universe, will be released on February 14, 2019.