I like to rag on Amazon as much as the next guy here, but this article seems a tad misleading. They do still show up when you plug them in. The article even says they use MTP now instead of functioning as a direct USB mass storage drive, which means you can still plug them into your PC and transfer files though File Explorer. Android handles USB file transfers the same way, and that works fine.
………. So is there any attempt by Amazon here to limit users transferring their ebooks to their computers?
In short, no.
What’s changed here is now the Kindle and PC will actively communicate with each other during file transfers with MTP instead of the Kindle “pretending” to be a USB flash drive with USB mass storage. There are some important trade-offs that come with the switch to MTP but nothing that will stop you from transferring ebooks to or from a computer.