If ``recline_preview`` extension is new in CKAN 2.0 it should be:

    .. versionadded:: 2.0

just before the docs about the recline preview extension.

If I understand the second sentence properly, it used to be possible to embed Recline previews, but from CKAN 2.0 onwards this is no longer possible? In that case add a separate note:

    .. versionchanged:: 2.0
       It's no longer possible to embed Recline previews.