There was news a few months ago that Teller (of Penn & Teller) was working on the effects for a stage version of The Exorcist. His skills at illusion would certainly make a theatrical version most scary.
The Geffen Playhouse in Los Angeles is producing the show, John Doyle is directing the show and John Pielmeier is writing the show.
Now the Geffen Playhouse website has a bit more info.
The most chilling test of faith come to life on stage. This world premiere adaptation of the famous 1971 novel documenting the terror and redemption of a ten-year-old girl remains as frightening and relevant as when first experienced. Under the direction of Tony Award winner John Doyle and adapted by acclaimed playwright John Pielmeier (Agnes of God), The Exorcist transforms the unsettling battles of good versus evil, faith versus fact and ego versus ethos into a uniquely theatrical experience as sophisticated as it is suspenseful.
I wish I was in LA next year to go see it.