Amazon to pay Kindle authors only for pages read

Scalzi has a good take on this: http://whatever.scalzi.com/2015/06/21/amazon-tweaks-its-kind...

Notable is that Amazon still sets the overall amount that all authors can be paid -- the pages money comes out of a pot, and Amazon sets the pot. Also, he brings up the idea of a "choose your own adventure" book -- it's not yet clear what the payout would be in this case.

This is only for Kindle Unlimited.

Scalzi points out that he doesn't view Amazon as evil, but that there are situations in which Amazon acts more in its own interests than those of authors.

This is for self-published authors, but how long until Amazon will try to force it to regular publishers too, perhaps with some algorithm to even include (re-adjusting price as data come in) regular pre-paid books?

It's also a bad precedent for Spotify and co (to not pay for tracks skipped mid-way etc).

Finally, what about books that are meant not to be read in their entirety, like any kind of reference book?