I think more people will get into digital only trends as economies and technologies become easier and cheaper to develop/own next, next gen, but a physical copy of game will always be traditional practice.
There has never been a successful console or period of gaming history that was "digital only" and I don't think major corporations are willing to bet on a next, next gen console that doesn't at least offer the alternative physical option. Playstation and Xbox would miss out on a HUGE profit if they went digital only across the board. Sure, a slim version or "pro" version of their console can be digital for form and factor reasons, but there will always be the disc friendly machine next, next gen.
People still collect games, and fast/high speed internet access is another thing that many gamers don't have. I certainly wouldn't like it if physical games disappeared even though like 80% of my PS4 games are digital lol. A major part of the gaming experience is actually holding the thing in your hands, keeping it on your shelf, flipping through the covers and artwork.