If I recall correctly, even Blatty said Friedkin agreed to direct.
Just havin the teleplay doesn't guarantee production, though. WB/Morgan Creek would need to come on board and cough up the money to get it filmed, and that's no cheap feat. THEN they'd need a network to air it. And I don't know many advertisers that'd want their product going to air after the crucifix scene… The Exorcist is a hard sell, especially on TV.
Hopefully, a network takes the gamble. I'd love to see HBO or AMC give it a go.