The latest version (2.3) was released in 2013-03-20 and it is compatible with the confluence version 5.5.6.
I would think that this version is also compatible with the 5.6 but was not updated in the Atlassian market place yet. As far as I know, there's no ETA for this plugin to be released a new version.
I recommend to go to the page: https://marketplace.atlassian.com/plugins/com.atlassian.confluence.plugin.copyspace/versions and click on watch this plugin to receive updates of new versions and compatibility changes.
Please, vote and watch the following issues:
Vote & Watch!
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