I recently developed a (non Amazon!) plugin for
KOReader, called Dynamic Xray. The main difference with Amazon X-ray is that this plugin allows an user to
dynamically define descriptions for persons, locations and terms, while reading. These descriptions can be assigned to a single book or to an entire book series.
On
GitHub you can see screenprints and -casts of this plugin in action (most recent and therefor up-to-date developments at bottom of the discussion).
I publiced the code of the plugin in the
GitHub Dynamic Xray Repository.. As it is now integrating this plugin into default KOReader code will require some programming experience.
Alas, I don't have time to provide support for this. But I hope the KOReader developer community will integrate an adapted version of this plugin into the default KOReader installation.