@sbarnhar: If your get new Kindle that is still on fw 5.6.5 you can
jailbreak it and have Calibre (via Kindle Collections plugin, just like before) generated collections
imported to your Kindle by using
LibrarianSync KUAL extension on your Kindle.
The difference is that extra step / extra requirement of using LibrarianSync to import Calibre generated json file to device's collection database/catalog, instead of Kindle Collection plugin directly manipulating device's collection data/ json file... (And maybe Kindle 3 didn't need to be jailbreak-ed to be able to use Calibre plugin, because collection file was on /mnt/us/system ?) if I'm remembering my Kindle 3 days correctly.