So your example for something that could replace Amazon... is Amazon?
Amazon is doing at least two things really well that is going to be completely impractical for individual self-publishing authors to do on their own: Providing a go-to place for customers looking for books, and payment processing.
Yes! ;-) The example was used to refute the fact that authors are technically incompetent. In the next generation most people will be able to put together an ebook.
I think the threat to Amazon will come first from best-selling authors, who already have a faithful following of their own. For everybody else, Amazon is great, for now.
But imagine a future where a search engine can help you find great ebooks, and where a simple payment system can let you buy them directly from authors (charging 2-3% to authors) -- why would you need Amazon then?
You just described Amazon. On top of that, they have the recommendation engine, public wishlist, affiliate program, and allow you to buy all kinds of other products via the same UI.
It's going to be very, very hard for any competitor to become attractive enough for customers to matter. I don't think even best-selling authors can just ignore that factor.
The new generations of authors will be very tech-savvy, to a point that may sound incredible now but is very real.
And even if some, or the majority, of authors don't want to do this themselves, why can't they hire a bunch of folks to do it for them? Why would they hand over 70 to 85% of potential returns to a publisher or to Amazon when they can pay someone a fixed price for editing, proofing and page layout, and keep 100% of the returns after that?
Publishers are clearly doomed since they don't provide enough values for the fees they demand; but I doubt Amazon's position is a lot more secure.