What types of data is available to collect from a Kindle, assuming of course the device is used for nothing but reading ebooks?
IP address and location as you move from place to place (LTE/wifi).
Reading habits and library
Political leanings
Other associated metadata that may do more to link that device to your overall advertising profile and help deanonymize you for other data brokers.
Another commenter lists a few options, but even the most basic of data - what a person chooses to read - is personal and private enough to warrant caring about.