A lot of this has already been said many times, but it is always good to remind yourself of how fast things can go.
Our engagement is now defined by push-driven notifications rather than the traditional pull-driven experience
"Defined" here is a bit strong, and so is the title using the big word "next". We are definitely not there yet. Sure, notifications drive engagement to content, but many of the content discovery is still a pull-driven experience (best example is probably Instagram). Just look at what people do when they don't have anymore notifications to check…
One way of discovering content doesn't have to die for another to flourish. Both can—and will—coexist.