Google have just posted about new update to mobile friendliness indicating that in order to provide good user experience on mobile devices app install interstitial can not any longer cover/hide significant amount of the on-page content.
“Starting today, we’ll be updating the Mobile-Friendly Test to indicate that sites should avoid showing app install interstitial that hide a significant amount of content on the transition from the search result page. The Mobile Usability report in Search Console will show webmasters the number of pages across their site that have this issue.”
In terms of the timeline for this update Google says that after November 1 any mobile web page that show an app install interstitial that hides a significant amount of content on the transition from the search result page will no longer be considered as mobile-friendly.
Google won’t punish sites using the standard app install banners in Chrome and Safari; this is aimed at the huge annoying overlays purposely blocking access to the desired content.