User blog comment:Rappy 4187/Technical Update: May 4, 2015/@comment-5558012-20150506160241/@comment-957747-20150506165526

I'm sorry. I thought I was clear. The feature is being removed from Labs for the moment. If it is not in Labs, it cannot be enabled. Once we're done with the behind-the-scenes updates, it will return to Labs. Until then, if disabled, you will not be able to re-enable the feature because it was removed from Labs (this actually was said in bullet point 3 below).