Now, I'm not saying that WotC shouldn't do their own stories or write what they want. But they do *need* to listen to their audience, and see what the audience wants to buy and play. That's key. A couple years to get a feel for writing storylines and establishing the process is fine, along with letting people get a feel for the game. But, after that, they really need to take stock of what there's a demand for at that moment, what can wait, and what people don't really like.
I probably overstated when saying I don't want WotC listening to customer feedback on stories . . . but I don't want them to rely on feedback on story telling, as I feel that can overly limit creativity. It's why we got "Dragon Magic" in 3E, and why certain story elements get beaten to death and become tired (not just D&D, but in general).
While WotC has revisited Magic story lines in the past, and is doing so again this fall, they won't necessarily be telling the same story again. Same world, probably some returning characters and villains, but a new story. It's a sequel, and there's nothing inherently wrong with sequels, although they are often screwed up (or prequels, right my Stars Wars brothers?!). We've seen other properties fail by over relying on sequels rather than pushing forward, hopefully this won't happen to Magic. They've got that game down to a science over there at WotC, so I'm not overly worried, but there is always the chance . . .
D&D has been mining the nostalgia vein for quite some time now, and it IS starting to get tired, IMO. I'm not sure it's tapped out yet, but "looking backwards" is a part of D&D's DNA at the moment. I'm excited for Elemental Evil, but I'd rather see something new. If the next few story arcs continue to mine things we've seen before several times each in previous editions, my excitement will likely wane. Although, if they do a bang up job, my interest might be kept despite the over reliance on nostalgia. But this is another area where WotC can do no right. We have some fans bitching about tired rehashes, and others bitching about why THEIR favorite setting/story/characters aren't being released for 5E NOW!
Paizo has truly been very successful, and WotC I'm sure has taken note. But mimicking Paizo's style isn't necessarily the way to go. And I think we're looking at Paizo through rosy colored glasses, and at WotC through dark sunglasses. Paizo may have designed their Kingmaker story in response to a fan desire for more sandbox style play . . . but that isn't STORY, that's GENRE (and not story genre, but gaming genre or style). The Kingmaker story itself wasn't designed on player feedback (to my knowledge).
Note: You're right, Dragonlance came about in part because there was fan noise about not enough dragons in Dungeons and Dragons! And the genesis of Dragonlance was very much a marketing driven thing, Weis & Hickman being ASSIGNED the novels rather than the story springing forth from fertile, creative minds. Dragonlance was very much created by committee. I enjoyed it so much as a kid, I had forgotten that. But still, the directions Weis & Hickman took that story outpaced it origins by committee, IMO.
Note: You are worried about WotC relying too heavily on old stories, so am I. But isn't Paizo doing exactly that RIGHT NOW! They are just launching the next AP "Giantslayer" which is coming across as their own version of "Against the Giants". I find that interesting. Don't really have an issue with it, and I'm sure Paizo will knock it out of the park.