This does point towards Jekyll filling a Nick Fury role in the series, with The Prodigium almost acting as S.H.I.E.L.D., bringing together the disparate monsters into one big story. While it’s not what Robert Louis Stevenson probably had intended for his legacy, it makes a lot of sense for the character’s involvement here; having a slightly stronger evil side doesn’t match immortality or becoming a literal wolf.
That said, because the film is dealing with such a well-known character – the twist with Jekyll is so iconic it’s legitimately OK to spoil – played by an Oscar winner, there was still a concern that Crowe’s presence could overshadow the main events of the movie, leading to the filmmakers striving to work him into the story more organically:
“If we’re going to bring in Henry Jekyll, how is bringing Henry Jekyll into the mummy story not detract from the mummy story? How does Henry Jekyll become part of this story in an organic way? And part of what Tom’s character, Nick, learns about the mummy and about the history of the mummy comes through Jekyll’s very deep understanding of monsters and how monsters have existed quietly in this world for eons.”
Bringing in such a big character into a separate movie could easily feel like simple franchise-bait and ring cynical, so this concern being addressed at his introduction is refreshing. It is, of course, unclear how much presence Jekyll will actually have in the film – Crowe only appeared briefly in one location in the trailer and as the character didn’t always fill this narrative role, he’s unlikely to be focused on too heavily. That makes it seem unlikely we’ll get to see Mr. Hyde in the flesh, although who knows what tricks The Mummy has up its bandages.