Google has officially confirmed the intrusive interstitial penalty went live on January 10th. But, the full effect of this update hasn’t been recorded by webmasters just yet.
As mentioned by Google, this penalty will only impact intrusive interstitials that happen after going from the Google search results to a specific landing page. However, it will not impact or penalize any other pages after that.
As reported on Google Webmaster Central Blog, here are some examples of techniques that make content less accessible to a user: