As of September 21st, we can now offer our KDP self-published books in hardcover, not just softcover! This is the first major tangible improvement to KDP since they acquired CreateSpace's best-in-class print-on-demand capabilities, expanding "Kindle Publishing" from ebooks alone to both ebooks and paperbacks... and now, finally, hardcover!
Of course, this is still POD, so it needs to be kept pretty simple to minimize production costs (and production errors). So, no dust jackets or embossing: the hardcover they now offer is like a hardcover textbook, a "case laminate cover" made by wrapping a water-resistant laminated printed cover image around two pieces of very dense cardboard ("caseboard") and the spine binding (the part that holds all the pages together). It is available in only five trim sizes and requires a minimum of 75 pages.
Naturally, this casebound hardcover will cost more than printing it as a paperback. Amazon still intends to give you ~60% royalties from every sale, though, so 100% of the higher cost gets passed along to your customers... which means if you want it to seem affordable, you'll need to list it very close to its minimum cost, and earn 60% of a minimum price. Still, it's your book in hardcover, without all the hassle and expense of doing a print run and dealing with inventory!
And it seems that Amazon has worked hard to roll out this new service as widely and conveniently as possible: right from the start they are offering two different hardcover finishes and three different interior paper types (the usual white or cream-colored paper and a premium paper to maximize interior color image quality—so no real changes here), and global distribution. They have also released a cover template generator tool that will make it much easier for cover designers to get this new format exactly right. You can even use it to design your own covers, but unless you're a graphic artist familiar with the demands and conventions of book-cover design, you'll be better off hiring a pro.
I look forward to ordering a hardcover KDP book and seeing for myself the kind of production quality they are able to offer!