One example of this evolution is popular "will they? / won't they?" pairings. In the 80s with Sam & Diane or Dave & Maddie there was considerable audience pressure to resolve the romantic tension and get them together. Since serialization was in its infancy this wouldn't be much of a process, more of a one-episode switch from "a show in which two people flirt" to "a show in which two people have a relationship" (although Cheers, to its credit, managed to carry out these things in nice season-by-season steps that neither required viewing every episode nor felt arbitrarily static).
The big pairing of the 90s, at least in my crowd, was Mulder & Scully from The X-Files. The pressure was certainly still there on the audience side, but the fate of the previous shows (growing irrelevance for Moonlighting and many interesting but difficult contortions for Cheers) led to an extreme awareness on the part of the creative team that putting Fox & Dana together should be done very carefully, and at just the right moment. And while this moment never arrived, at least on TV, its inevitability is demonstrated both by the extreme non-starterness of both characters' outside love interests and the fact that no justification was felt necessary when they're suddenly living together in their second movie.
As the 21st Century approached, the concept of "jumping the shark" passed into popular parlance (again, at least in my crowd), and with it the sense that resolving a situation could wreck a show. And this extended beyond romantic pairings: everyone had seen and minutely examined the fate of Twin Peaks, which had been designed to be all character exploration with no plot movement, when it was forced to resolve its central mystery (in short, a burst of brilliance followed by a quick, uneven, fall).
Therefore, hyper-self-aware shows like Xena: Warrior Princess and Buffy The Vampire Slayer played with the expectations, either by teasing developments they had no intention on delivering or by bringing the consequence of "giving in" to such impulses into the show's narrative.
So in these and many other cases, the creative teams had learned that sometimes it was vital to deny the audience what they wanted. Of course, there had always been some awareness of this; everyone knew that if you exonerated The Fugitive, cured The Incredible Hulk, or let the kids escape the realm of Dungeons & Dragons that would be the end of the show, but the audience knew on some level that these things could never happen short of the finale, whereas now the audience was being denied things they might reasonably expect to happen.*
The next stage of evolution, therefore, had to be on the part of the audience themselves. Many people were probably aware, on some level, that the show was better off if Buffy & Angel didn't live happily ever after, but the yearning for it to happen (or some substitute involving Spike or another known character) was still plenty strong. It took a further step for people to just stop even inwardly wishing for that kind of development.
The first big case of this to catch my attention was among the fans of Elementary, the American modern-day Sherlock Holmes show. Almost from the beginning there was a strongly expressed wish that Johnny Lee Miller's Holmes & Lucy Liu's Watson NEVER get together romantically, one that would have been hostile even to flirtation or hinting, and to the show's credit there wasn't any (compare with the BBC series Sherlock, which engages in some self-aware teasing along the lines of Xena & Gabby although with a very light, ironic touch). And it's not just that this audience didn't want it to happen; they were afraid that it would happen someday in a misguided play for ratings.
I noticed a very similar reaction, but on a plot rather than character level, to HBO's disappearing-people show The Leftovers. It generally takes a few episodes to figure out what the show is doing, but once people get hooked they often express a wish that the show stick by its practice of never explaining any of its seeming supernatural events, even to the extent of definitively proving that they ARE supernatural. I've seen many posts that quote the refrain of the 2nd Season theme song: "Let the mystery be"; they wouldn't wish for a big reveal any more than you'd wish for a juggler to stumble while he's trying to keep pins in the air.
I think this is great. Not that all shows have to be like this, but I love that a sizable audience has learned that a good cross-gender friendship or an insoluble mystery can be beautiful things, which would be spoiled by a resolution. In a way, it shows three stages of wish fulfillment: This audience went from wanting something without knowing it was bad for them, to wanting something while knowing it was bad for them, to NOT wanting something they knew was bad for them. And just because in real life they might wish to know if miracles really happened, or what it would be like for that co-worker to make out with them, they no longer required their tele-fictions to fulfill those wishes within their stories. At least, not every time.
Examples, counter-examples, and any comments always welcome.
* - Of course, another direction to go with either romantic tension or mystery is to resolve it and move on without making it a big deal. The 4400 was good at both of these; the leads determine their mutual level of attraction early on and never deviate from it, while the plot mysteries were resolved at the end of each season in order to make way for deeper ones in the next. Community might also qualify; characters get it on when they naturally would do so, without this upending the more important relationship in their life: that of the study group.