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New Kindle e-readers no longer appear on computers
(goodereader.com)
This is a most excellent place for technology news and articles.
Seems like they don't work exactly the same as they used to, as they now use MTP instead of USB mass storage, but while annoying, it's generally a pretty trivial fix and your OS may already use MTP devices with no trouble. It seems there may be some other knock-on effects with fonts not sideloading right and needing a Calibre plugin to make pagination work how it used to.
So yeah, it's getting worse, but Amazon hasn't figured out how to bring the hammer down yet.