Some blogger writing about the Ransom Model analyzed King's model for "The Plant." If he had a good grasp on its principals, it's a flawed tool. The way "The Plant" thing worked was that anyone could download a chapter for free and you could pay for it afterwards. If a large enough percentage of the downloads were paid for, King released the next chunk.
Now, you can see how a hater with some scripting skills could just build a 'bot to download it continuously without paying, right? But the bigger flaw, from my perspective, is that it punishes the legitimate buy-and-pay users. Collective responsibility works okay when there are some limits to who's held responsible. The Ransom Method in practice has been nearly Christian, with a few hundred people paying for the downloads of thousands.
Why do I think it'll work with serial fiction? I don't know, but I'd like to think the following factors are in my favor.
1) Readers are invested because there's a chance of seeing their idea incorporated.
2) Readers are also invested because of the uncertainty. Will the next chapter emerge? It's not like a book where you can put it down and be sure it's going to be there when you come back. You can influence the outcome, however... though it'll cost you.
3) Readers are ALSO invested if I use a cliffhanger model to build suspense.
Think of it this way: If there was a magazine that was serializing a long work by your favorite novel, you'd buy every copy even if the rest of the magazine didn't do much for you, right? This doesn't cost as much (or necessarily anything every time) and you don't have to put up with ads, either.
If I recall correctly, $15 is not only the average, it's also the median, for what that's worth. And it doesn't necessarily have to be 600 donors. I expect some people will only donate once, while some will probably be repeat customers. But I don't know. I guess we'll have to wait and see.
What's surprising so far is that so few people have sent in ideas. I mean, that's the part that's FREE. X, did you send one in? If so, I didn't get it.