I think Penguin made the right call regarding Gerald's Game and Dolores Claiborne. I remember King's notion back then, and it really didn't make sense in terms of the literature involved (and I think it shows, too, that King actually enjoys marketing and tailoring product to fit certain sales goals; nothing wrong with that, as it in fact is simply another form of creativity; I enjoy it when King comes up with schemes, truthfully).
King's experiment with Desperation and The Regulators was fun and interesting, except for one tiny (read: big) thing: there really wasn't a strong enough connection between the two. The set of characters in one tome should have been the same in the other, and should have realized it at some point. In fact, although this would have been tough to pull off, imagine if, at one point in both books, each character realizes what the other is doing (and has done and been through) in the other world, and how it relates to the respective current situations? Makes one's head spin, but it could have been done, especially if, perhaps, Tak/Seth was actually a malevolent god-author that intended to place the characters into other books as a sort of Hell-punishment. (Maybe all the characters could have died and been sent to those books.) This could easily have led to a Dark-Tower connection (if one doesn't already exist).
I agree, though, that it would be great to see some new marketing gimmick from King. Would love something like a dark quartet of novellas that were sequels (or stories set in the same world) to previous novels. Could be called To Be Continued... perhaps (or, Dark Quartet, come to think of it, if that title hasn't been used too much already). Although that isn't really a gimmick, I suppose. Maybe King could do a multimedia trilogy -- starts as a book, then it is a movie, then it is a quality TV series on AMC. Of course, that isn't an original idea, as it echoes the model some in Hollywood wanted to employ for the Dark Tower series. And if you want to cut costs, how about a book, a short film sold at Amazon (or YouTube), and a series of digital comics?
How's this for a gimmick? King writes a collection of stories called Dollar Babies. This collection would harken back to the tone of Night Shift. It is promoted with the intent of generating many short films based on the tales. They all find a home on this site (or if YouTube were to be used, the links would be curated here). All the dollars collected would go to a charity, or support libraries, whatever. Or, if it isn't meant to be a charitable device, King could sell multiple licenses to each of the tales, with some commercial ones going for a few thousand a pop. How much money would that bring in?
You know, although King probably would never do something like that, especially since he's older now and probably just wants to write and let others think of marketing angles, I honestly wonder if say someone like Joe Hill, who is younger and still starting out, would employ such a model to increase his brand status. As media evolves, one wonders if stuff like this will happen.