I'm attaching a beta-version of the plugin.
It's based on version 0.73 of the core, stand-alone KindleUnpack "engine." Because of this, there are some new settings available (check the plugin's configuration) concerning HDImages and the type of ePub output.
But in addition to that, the plugin has also been ported to (hopefully) work with the future (PyQt5) version(s) of calibre. So if you're using/testing the beta versions of calibre, make sure to give me a heads up if you run into any issues.
It should stay compatible with the current (and earlier) version of calibre as well, so I'll need to know about any problems there, too.
Basically let me know if you have issues.
(and let me know what version (beta/release) of calibre you're using)
If all goes well, I'll make it an "official" release.
EDIT: Pulled the trigger and made the beta the official release. Removing beta attachment. See first post to download the zipfile.