Its functionality was initially part of JM Canonical plugin (for testing and saving time), but now we moved it to separate plugin.
JM GSitemap plugin 1.0
This plugin is not a replacement of core plugin; no core changes are needed. It just saves the time of manipulating with sitemap entries and fully support HTML sitemap version. It uses new Admin UI so that you can use searching, filtering, ordering and functionality of batch changes.
With core plugin, you have no option to change the category, but it was used without user see it.
More instructions about HTML sitemap.
Yes, there are plans for further extending, but at first JM Canonical plugin must be cleaned more and we need to do something with metatag plugin.
This plugin is free; just it's download is limited to user subscribed to class JM Canonical plugin (or something like that).