Services and convenience
Networks used to hawk phones to pimp their technology: SMS, MMS, 3G, GPS, etc. It then used to use new phones to pimp renewals as way of keeping ARPU up. Now that so many of us have phones that are good enough, the codependency no longer makes sense. This should cause networks to start pimping their services as T-Mobile had done in the US by partnering with providers to promote an "unlimited" service with lower bandwidth. We'll see more of this with vertical integration and deals providing the cross and upselling for higher margins.
There's still money to be made in handsets, as the volume of high-end sales shows, but as the article points out, manufacturers may have to compete against themselves to make sure they get the customer.
There's still a lot of room for technological advances in handsets: better battery life, screens that cope better with ambient light, foldable, etc. but this may mean the risk of fragmenting the market. Still the ubiquity of the modern mobile phone highlights its importanct and, hence, sustained demand. It just won't be driven by contract renewals.