I think this discussion is giving Leonard Katzman at that time too much credit. Any longterm planning at this stage is very unlikely (imo). Decisions seem more and more to be made in passing.
Allow me to elaborate:
The previous dream season had many faults (international focus etc.), but they didn't drop any storylines because they did not know what to do with them anymore. Even the whole Marinos storyline (which I disliked) had an arc of suspense which culminated in the season's finale. That's why I regard it as granted that Ben Stivers would have turned out to be Jock (with Capice in charge and Duffy still out of the picture).
In a series like Dallas, which is supposed to feel like a saga, longterm planning should dominate. That's why the loss of Ewing Oil in the season's finale for example feels like a storyline coming full circle.
Interestingly season 9 (dvd 10) started and ended with two unsatisfyingly written storylines. Granted, for the first one (Bobby's return) Katzman didn't have much time, but for the 2nd (Pam's exit) the writing was very poor.
In between we got the Wes Parmalee storyline. I disliked the initial writing there because they didn't even bother to change anything - again we get a suspicous ranch foreman hanging around the Southfork living room, staring at pictures, something we have witnessed the last 4-5 episodes. It's beyond me why they gave him a new hair colour and a different name.
Back to your topic:
I don't "think" that Katzman intended making Parmalee Jock. In order to make it captivating (which it was) we got all the lie detectots, x-rays, etc. I had no problem that they left the storyline ambiguous, but they just dropped it, never mentioned it again and just forgot about it.
Katzman probably discovered a week prior that Steve Forest is not available anymore (during his Gunsmoke movie). If you have to drop it, at least don't plant seeds insinuating to continue the storyline. I hated it that Clayton threatened to kill him and everything is forgotten after two weeks like nothing happened.
But that requires longterm planning.