https://phabricator.wikimedia.org/diffusion/EBUR/history/master/ shows that this was imported from "svn.wikia-code" by @ashley.
Cannot find Tim Weyer/cervidae or SColombo (mentioned on https://www.mediawiki.org/wiki/Extension:BatchUserRights ) in Phabricator.
Per https://github.com/Wikia/app/blob/dev/extensions/wikia/LICENSE , the extension should be licensed under GPLv3+.
The extension was removed as unused from Wikia's repository in October 2015.
Note that my comment specifically applied to the Wikia codebase and only that codebase. Wikia's version of MediaWiki -- if it can even be called that anymore -- is a highly customized version based on MediaWiki 1.19 and subsequent modifications.
Wikia considered the BatchUserRights extension useless for their purposes in 2015 and thus removed it from their repository, presumably so that their developers don't waste time maintaining it; it may or may not have other third-party uses and users, however, and we should take that into account before considering archiving it.
BatchUserRights probably needs at least some cleanup before it can be considered useful and usable, though; such as adding support for expiring user groups (T157015), a new feature in MW 1.29, and replacing deprecated method calls (e.g. OutputPage#readOnlyPage and whatnot) with their non-deprecated equivalents.
cc'ing @Mainframe98 for further input and thoughts on what to do with this extension.
Thanks @ashley. Yes, the extension may need some work to make it usable again. With it now converted to extension registration, it is ready to support the new MediaWiki versions, but it'll need an active mantainer.
Thanks for clarifying @SColombo.
All: shall I add COPYING file for past REL1_* of this extension with the contents of the GPL-3.0? It seems we've got content from REL1_19 in advance. Thanks.
@ashley I can imagine the relevance of this extension only increases if it's able to add expiring user group memberships. It seems easy enough to update this extension to support expiring group membership, I'll probably convert it to OOUI too while I'm at it. According to WikiApiary the extension is still in use. I don't know if those numbers really are a good indication though.