On February 26th, Kindle customers will lose the ability to download eBook purchases directly to their PC. If you want to switch to a rival eReader brand in the future, I suggest that you use the soon-to-be discontinued “Download and Transfer via USB” feature to archive your Kindle library.
Unfortunately currently broken for the latest version of Kindle for PC, which switched to a different encryption scheme. It also uses KFX file format that nobody likes, which fortunately can be converted to EPUB with another plugin, but de-DRMing doesn’t seem to work right now. It still seems to work for titles in AZW3/MOBI that didn’t get DRM update or didn’t have DRM in the first place.