This is a very good question.Computers reached a point where updates were not a gamechanger for most of the market, just at the point when smart phones were blossoming. But phones are now reaching that same plateau. Will Apple turn to a new area when that happens? Or remember their core market?
Computers still remain a large market, one that Apple were gaining a larger share in. Is the R&D such a burden that they cannot regain that momentum?
Apple has (so far) still been making pretty significant year-over-year improvements in their Axx SoC line; but that will (soon) reach the same plateau that Intel has reached with their CPUs, and to some extent, that NVidia and AMD are reaching with GPUs. This should translate into Apple still having a few more years of significant improvements in their mobile devices. But as far as the Desktops (and Laptops) go, everyone (not just Apple) is pretty much just rearranging the deck chairs on the Titanic at this point.
Does this mean that "PCs" are dead? Not by a long-shot; but it does mean that everyone (not just Apple) have to start thinking further and further outside the box in order to keep enticing users to Upgrade those items.
Fortunately, if anyone is "routinely disruptive", it is Apple; so I feel confident that they will continue to lead the industry around by the nose, and, so long as they don't get too far ahead of the industry, like they did with the "trashcan" Mac Pro (thinking that they could "force" TB adoption faster than it has happened), the industry will continue to follow Apple's lead, which is good for Apple, and ultimately, for the entire industry (not to mention you and me)...