Regarding "Stephen King" as a potential IP -
1) I'm not suggesting an entire land dedicated to Stephen King. One ride is not going to jeopardize the "family friendly" atmosphere of the entire theme park.
2) Universal Creative could do almost anything with the IPs. They wouldn't be forced to include the "elevator with blood" scene from The Shining. They could do something as simple as a Pennywise (It) thrill ride... not suggesting this is a great idea, but they could easily retheme Dr. Doom's Fear Fall into a Pennywise's Fear Fall.
3) Considering Stephen King's popularity and Universal's precedence of either working with him or previous plans to work with him, Universal reaching out to him to partner for a theme park ride is at least possible.
Please note that I'm not some super-fan of Stephen King... there's tons of other IPs I'd rather see. I'm just saying that it seems like it might fit in the Monster's section, especially if they start looking to expand the area.
That's good to hear, since the Mummy is terrifying: two people murdered, several references to death, a walking corpse makes several attempts to kill the riders, and the ride features stereotypical phobias including the collapsing ceiling (claustrophobia), bugs, fire/explosions, darkness, and high speeds.