A simple extension for SilverStripe 3.1 that restores the status tag behavior of sapphire framework 2.4. Needs SiteTree::add_extension('PageStatusExtension'); in your config.

PageStatusExtension

class PageStatusExtension extends DataExtension {

	private static $db = array(
		'Status' => 'Varchar'
	);
	private static $defaults = array(
		"Status" => "New page",
	}

	public onBeforePublish($original) {
		$original->Status = "Published";
	}
	public onBeforeUnpublish($original) {
		$original->Status = "Unpublished";
	}
	public onBeforeRevertToLive($original) {
		$original->Status = "Published";
	}

}