This change IS a pretty big deal for indie writers. Amazon announced today in their KDP newsletter that they have updated their recommendations for cover sizes for Kindle ebooks.
The new guidelines are a minimum of 1000 pixels on the long side - although they "recommend 2,500 pixels on the longest side to ensure better quality, and an ideal height/width ratio of 1.6."
So to break this down, if you go with the minimum, your new image size should be 625 pixels wide by 1000 pixels tall. If you jump to the recommended level, to retain a 1.6 aspect ratio, you want an image size of 1562 pixels wide by 2500 pixels tall (roughly).
While the smaller size is pretty typical of what many indies are already using for cover images, jumping to the recommended level will often mean paying higher prices for art. Jumping an image from 1000x625 to 2500x1562 isn't just a matter of expanding it in your image editor - that way leads to pixelated, ugly looking images. Instead, you need to go back to the source art and use larger source art. Both royalty free art sites and artists for unique art will generally charge more for larger images, and in some cases artists might not have larger source art available for an image.
It's not the end of the world, but it's something indie writers need to pay attention to moving forward. Screen quality is only going to continue improving on ereaders, which means images with higher pixel counts are going to become desirable. Plan accordingly, and build your cover images with higher resolution than you intend to use.
A last note on this: these images are the display images Amazon uses to sell books on their site, NOT the cover image included in the book. In most cases, it is advantageous to include in the book file an image on the lower end of the spectrum, since readers will rarely actually see it there, and higher quality images result in a larger files size for the ebook. Since indie writers getting the 70% royalty from Amazon are billed a small amount for file downloads, the bigger the file, the less you earn per sale. Those pennies can add up in the long run, so best practice is to include in the book file a smaller file size of image than the one you're using for display.