HBASE-4811 "Support reverse scan" was implemented from version 0.98.0, and is available in the Java API.
However this functionality is not yet exposed via REST.
Example of expected API call:
(Returns rows ordered by key in reverse, eg from 9*** to 1*** )
Based on my (limited) understanding this should be simple to add.
This function creates a Scan object with parameters passed in from the REST API (I assume).
Adding this functionality may be as simple as adding a "reversed" parameter to the REST API which passes down to where the Scan object is created in TableResource.getScanResource.