It's interesting you mention this as CBS did run ads along the lines of, "Dallas is entering the '90s," and, "Women are strong on Dallas now," but it just wasn't going to matter. Dallas was too identified with the '80s, and JR, who was not in any way a '90s character.
Knots didn't have the same dating problem, as it just wasn't as publicly defined (when I was growing up my family watched Dallas and Falcon Crest but never mentioned Knots), but I think most of the characters just didn't have any real life left in them by 1993. They could have tried a show with some of the younger crew, but they had all been written out or just weren't well-developed, aside from Paige, who probably wasn't going to stay on much longer as Nicolette was trying for bigger things.
As always I am appreciating your rundowns, which give me a lot more insight into characters I wasn't very focused on, like Cathy.
If you ever get there I will be most interested in your thoughts around seasons 9-11 as those are not especially compelling years for me, with a few exceptions.