The days of "I-just-bought-an-Android-phone-now-I'm-getting-Google+-connection-requests-from-everyone-I've-ever-emailed" are over. Google has officially announced that Google+ will become an optional service and having it will not be necessary for using other Google services like GMail and YouTube.
While Google+ will still exist, it will no longer be a requirement for having a Google account. Users will also be able to create YouTube channels without needing a separate Google+ page for every one. If you have already created a Google+ account, you will be able to shut it down without affecting the services attached to it.
This means less support for the Google+ app too. They have even gone so far as to remove the Google+ app interstitial when users access Google+ from a mobile browser. Though, if Google can't have it than neither can you...
If you're unfamiliar with app interstitials, they are those buttons on websites that connect visitors to the App Store or Google Play, giving them quick access to downloading an associated app. Google revealed only 9% of the people who landed on their interstitial page actually downloaded the app, so they recently recommended not using them.
Google recommends a smart app banner.
It is unknown if having app interstitials will eventually lead to a website being filtered or devalued, but knowing Google, they certainly have a plan up their sleeves.