I very much doubt that this film will ever actually happen. They may well be planning it, but that's a million miles away from it going into production.
The Scream franchise worked very well and was responsible for putting the horror genre back on the map. However, horror has moved on from the 'pretty teen slasher' area and is far darker and more sinister. It won't be enough now to have a bunch of Dawson's Creek clones running around getting stabbed with a Scooby Do 'it was the caretaker' climax.
They would have to now parody the likes of Saw, Hostel, Wolf Creek etc and that would make it difficult for them to keep it linked with the first 3 films. What you'll be left with is a film that is so far removed from the others, that there's little point in giving it the Scream title.
I don't think getting Campbell etc on board would be too hard - they've hardly got glittering movie careers at the moment, but you'll know it's bad if they see a script and turn it down!
Having said all this, I'd much rather they do a new movie then remake any old classics.