I'm sure everything will be already scripted before the shooting begin.
I don't know how you come to that conclusion. Have you for instance seen Inland Empire and know about the production process for it? The fact that TPTR almost stuck entirely to a pre written script doesn't give any guarantees for future work.
I know about INLAND EMPIRE, but he didn't do INLAND EMPIRE for Netflix. Never in a million years Netflix, or Showtime, or CBS, would give Lynch 85m, or 50m, or even 25m, without a script (at least a pilot). More importantly, the shooting can't start if there is not a good chunk of scripts already in the bank (it would be dangerous because if in the middle of the shooting scripts aren't ready in time the shooting must stop).
But since Lynch won't work with a writer's room, with writers working while he's shooting (letting the show being wrote without him being in total control of it), you can bet that Lynch is going to start shooting with all the scripts already ready. Or a least a big, big part of it. Then of course he's going to improvise during shooting, rewrite stuffs on the fly, etc. He's Lynch. But it's not going to work like INLAND EMPIRE. It's a one in a lifetime experience. And honestly I don't think Lynch himself, let alone Netflix, would want to work this way again. I think he said that by the way.
Now that being said, I can be wrong, you never know with DKL. And I love INLAND EMPIRE !
I think it goes without saying that Lynch is going to direct everything. It's not an old format, like season 1 and 2, where there was a headwriter/showrunner and a writer's room, with the directors working for the writers.
As a small nitpick, there was barely a “writers’ room” in the traditional sense on TP. If you read the interview book with Mark, I don’t think there was any writers’ room at all in S1, just Mark reviewing and rewriting scripts. In S2, the “writers’ room” was just Mark, Harley and Bob (and later just Harley and Bob while Mark went MIA), with the writer-of-the-week sitting in for their episodes. Barry Pullman, Scott Frost, etc. were freelancers.
Yes, I know there wasn't a proper writer's room for Twin Peaks. But that's not really the point. What matters is the process (see what I answer to Soolsma just above). They were writers, which directors were depending on, because the shooting was happening while the other episodes were being written. Like a "classic show", where the showrunner is the headwriter. Most of the time, the rythm was dictated by the writers. Obviously, Lynch was sometimes able as a director to break free from that (see ep 29), but it wasn't a natural and pleasant thing for anybody.
That's why season 3 IMO was written like a big movie, before the shooting. So Lynch could direct all of it without being dependant on a writer. Frost this time wasn't a showrunner : he was just a co-writer (like Engels on FWWM). Because it was made like a movie, with the writing being done before the shooting. This way the director can be, like a movie, above the writers. And I'm sure Lynch is never gonna work any other way.