Edited to add:
I suppose the good news is that Amazon have a patent on this, which means that it's exclusive to them. So at least writers will be able to move their work from KDP to iBooks, Kobo and Nook, comforted by the knowledge that the other companies can't decimate their revenue stream by pedalling second-hand files...
Nope. Not if other companies buy a license to use a similar system or just do it and wait for litigation to sort it out, i.e. look at smart phone patents and that mess.
I still bet that in this closed system, it will be for store credit (amazon coins) not real money. So let's say Reader A buy's Cancelled for $3.99. She liked it, but wants to trade it in to get new books. Reader B wants to read Cancelled and has 5 Amazon coins. Reader B pays 2 Amazon Coins to Reader A to get Cancelled, effectively half price. Reader A can now spend those 2 Amazon coins to get a new book or buy another used book. Amazon's original cut on the $3.99 purchase was about $1.
Assuming a book can only be traded once (i.e. consumers can't resell the used content they buy), there is only $1 of the original purchase that could be used for the value of those 2 Amazon coins. Probably even less than that if you include the original cost of the purchase, which was probably a few cents for infrastructure, insurance, and other costs of doing business.
All in all, I wouldn't expect to get money for the resale of Cancelled since it's no different than a paperback resale which I can't control. All I can do is set my price at a threshold that accommodates an expected resale. I would expect to get money from Amazon if a user used Amazon coins to buy a NEW digital copy. Something like 3 digital coins new, offers of the digital file book used for 1-2 digital coins. The incentive for the reader would be buying it new, they could potentially get a portion of the credits back for something else, buying it used, they're stuck with the content (which is what happens with MOST used paperbacks, most are not sold over and over again but donated).
Another potential model would be like KDP Select. There is a set pot of money for content transfers and depending on how many times customers "Traded" your content is how much you get paid, because your content is valuable to the Amazon ecosystem of keeping customers USING Amazon devices.