What Could Have Been: In one interview, Alan Moore said that he originally considered having Irene Adler lead the team, but ultimately settled on Mina Harker instead because he worried that Adler was too obscure.
At one point Simon Bisley was considered for regular art duties on the book. It boggles the mind...
Stillborn Franchise: Apparently there were plans for sequels but since Sean Connery refused to do anymore of these films and the Director left directing. Not to mention that the film did less at the American box office and the production was troubled by lots of other factors, it's no wonder moral was dead.
Roger Moore was offered a cameo as Campion Bond, a part that was ultimately cut from the script, and would've been the first time two actors to have played James Bond shared the screen.
The ending cuts to Quatermain's hand coming out of the dirt and grabbing his rifle. A Call Back to what he said earlier in the film, "Africa will never let me die." But that wasn't used because they want to leave it ambiguous. At the least though it left the film open-ended rather then set up for a sequel that'll never come.