I'd love it if Rayne from Bloadrayne became a guest in MK and was somehow related to Nitara's story. If the vampire realm will exist (based on Nitara's story), there will also be vampires in Earthrealm (based on Rayne's story). Rayne's evil father, Kagan and her other half-siblings can try to destroy and take over both Earthrealm and the vampire realm while Rayne and Nitara stop them. If Nitara is evil, she could join Kagan and his minions on trying to conquer the realms. Something like that would give a reason why Rayne can be in the MK universe.