Google announced that starting November 1, 2015, mobile sites that have app interstitials that hide a "significant amount of content" will not be considered Google mobile friendly and thus won't benefit from the mobile friendly ranking boost.
This should come as no surprise because Google has said time and time again this is an issue. Gary Illyes said he wants it to be a negative ranking factor. They published a case study showing how they don't work as well. They hinted that this was something coming for some time now and even slipped up once about it.
The surprise is that this only impacts mobile sites that come from Google's mobile search, and then have this app interstitials only that cover most of the screen. It is surprising it doesn't impact all large ads that cover most of the content on your mobile site, no matter the format, the source and so forth.
Here is a sample of what is a mobile friendly and not mobile friendly app interstitial:
I can't imagine Google will stop here and only do this with apps.
The funny thing is that Google launched full screen in app interstitials as an ad format. I know it isn't mobile search but it is still very annoying.
In a Google+ thread, John Mueller of Google chimed in to clarify things already mentioned in the post. He said:
This is specific to app-install interstitials that hide a significant amount of content on the transition from the search result page. I haven't seen any cookie banners like that.
What about non app interstitials that are annoying? Google's John Mueller said they have nothing to announce now. He said:
At the moment, we don't have anything to announce with regards to other kinds of interstitials. We hear your complaints about them (and many of them bug me too), I'm sure the site-owners would appreciate your feedback as well though, so be sure to let them know too.
I wonder, seriously wonder, if this is one of the rare cases where the organic side of Google was influenced by the paid side of Google?
Forum discussion at Google+.