Wikisource has an OPDS (Open Publication Distribution System) catalog, which provides a way to directly download readable works from Wikisource.
The catalog is regenerated on a daily basis.
Adding the catalog to your device
The URL is:
Add this to your device's list of OPDS catalogs.
The catalog is provided by the WS Export tool. Bugs and feature requests can be filed at the Phabricator project.
Additional catalogs can easily be created for other categories; file a Phabricator task if you would like a new one added.