There was suppose to be a sequel in Falador. Had a halloween event years ago where we saw the Black Knight Castle is located in Falador. Sadly I guess it got shelved.
It is a true IM experience for everyone that plays that quest though.
There was never a planned sequel (just to be clear). The Falador seen in Invention of Disaster was solely created for that event. That isn't to say I wouldn't love to see the concept applied to other cities/locations, it was great fun to work on. Happy to see people enjoying it too! :)