I consider predictability as part of the genre. It may be good (J.R. getting close to bankrupt every now and then) or bad (Sue Ellen falling off the wagon always). I think I wouldn´t like it so much if it hadn´t this element. I find it challenging intellectually. Come to hink that most of 357 "Dallas" episodes ended with a cliffhanger...
You could predict the outcome or not, but it was part of the game. If it had remained self-contained, I´d have eventually get bored by it. Continuity made the show what it was, and it demanded attention from the viewer in order to keep the relationship with them going on. That´s why the Dream solution failed miserably: it demanded TOO MUCH from the viewer, ie remembering what had happened one year earlier.
If I have to be 100% honest, I think that killing off Jock was predictable, because Jim Davis had died, and primetime dramas didn´t recast its leads (back then). Also, Sue Ellen going back to J.R. and Cliff being ruined by J.R. before trying to commit suicide. This had the word "predictable" written on it. IMO, that was the first critical point of the show. Katzman & Paulsen saved it by creating the masterful storyline of the battle for Ewing Oil. Which was as unpredictable as it could be...
They were creating their own genre because there was nothing on primetime TV similar to it when they started. They had a modern day western family saga that utilized a serial format. That doesn't make it a soap necessarily because almost every show uses a serialized format today and they're not all soaps. Since they weren't following an established genre they were free to make it in the style they wanted. How much predictability the genre they created had was up to them.
Predictability can take a lot of different forms. The one I highlighted, the one that I think shortened what some call "the glory years", is the predictability of the characters staying very much the same as opposed to having long term character arcs where the characters develop and grow. Among the main characters there was very little of that.
The example of it were I really went into depth is the JR and Mandy storyline because it hinted at some character development for JR which would have really been a shot in the arm for the show, an injection of something fresh and new that would have created meaningful change. They hinted at it here:
JR: You know, all my life, the chase has been the most important thing to me. I'd be infatuated with someone for a while and when I achieved my goal, I couldn't wait to get away.
Mandy: (looks scared) JR...?
JR: Darling, what I'm saying to you is, it's different with you. I want you now more than ever. I cant't tell you what a wonderful feeling that is.
As entertaining a character as JR was, and he was certainly one of the most entertaining characters in television history, I think it was time for him to grow, to become a more mature, better man. I think they'd gotten about all the mileage of the conniving, womanizing JR who caused problems for the family as they could. Had they followed through with the change in direction in which they seemed to be going in that scene, it would have made Dallas seem fresh and new again. Instead of so much conflict coming from within the family - mostly due to JR's behavior, they would have had to have the main conflict come from outside of the family.
Wendell and Westar could have provided that along with Cliff working for Jeremy. Then JR becomes the protector of the family, since he's the oldest Ewing and more importantly, the one who would know how to use ruthless tactics against outside threats, but would only do so when absolutely necessary for his family's protection.
I described other types of predictability, such as Donna always being successful and always wanting to be able to keep Ray in "his place" as her cowboy. There's even a scene where she criticizes Ray immediately after he'd been involved in a successful real estate deal with Jock and Punk. Donna said words to the effect of: "It sure didn't take you long to become a Ewing did it? Just grab, grab, grab"!
They always had Donna pull that subversive crap with Ray anytime he ventured outside of "his place." It got tedious. She certainly didn't have a problem with Bobby and he was a Ewing! She was good friends with Miss Ellie, so there's clearly nothing wrong with becoming "a Ewing." The problem for her was Ray wasn't confining himself to strictly being a cowboy. It's irritating to see someone who lives to grab attention, grab the spotlight, chalk up success after success, and then watch her tell her husband he shouldn't do any of that. It's hypocritical, isn't it? She wouldn't have accepted being confined to one thing: Choose between being an author, an environmental advocate, an oil industry lobbyist, buying her own little oil company but only choose one!
They had Donna act like that towards Ray for so long that it was predictable when after he'd stepped out of "his place" and helped his brothers prove Jock wasn't a thief - something meaningful to Ray - that once again, she'd react poorly to his success. Yet she blamed their divorce on Ray being critical of her successes! Not only was it predictable she'd continue to apply that double standard, but as it continued it became not just tedious but abrasive! Anyone could have seen they'd inevitably divorce if she didn't stop that, and they did end up divorcing.
These aren't examples of repetitive, predictable things their genre necessitated; they just couldn't ever commit to having any of the main characters evolve and grow as human beings. Once in a while they'd hint at it maybe happening, but then they'd pull the character right back into being the same as it had always been.