Think theres a chance David Bowie filmed any scenes

He was due to turn up to film something but cancelled it (now we know why that would have been). Whether he made it on another day is yet to be known.

If he told Lynch then why he cancelled and without other cast members knowing, filming could have been arranged at another time to suit himself (like what would have happened with Catherine Coulson (the log lady). She was also dying and managed to fit a few scenes in, for which we should be eternally thankful to her.

Otherwise, it is just a case of using his character in the storyline without the actor, as they are dong with the original Sheriff Truman.

I don't think so. If they did, they would have had to keep it top secret. I don't expect any surprise cameos. Don't expect Bowie, Piper Laurie, Joan Chen or Harry Truman.

Hoping so, Babadook. That would be the icing on the cake, but I'm thinking it's more likely that we'll get a Babadook complaint thread about the lack of a Jeffries appearance, unfortunately.