I upgraded from an iPad Air to a 10.5" iPad Pro, and I still can't believe the MASSIVE, MASSIVE difference in functionality, screen quality, and speed. Love it.
The reason for this to stop though are not the same, before it was "tech limitations", which eventually get fixed... But the main problems now are economic limitations. The cost of going from one process to the next is escalating faster than the improvement in performance.
Considering people's money is not infinite and there less and less return in investment both for consumers (its good enough) and for the manufacturer, I think they will have to do something new.
Finding a way to parallelized more tasks is probably the way to sidestep some of the issue.
The fact that computers are less and less dependent on the central CPU and the rising importance of all those co-processing centers, means getting smaller as the ultimate goal gets less important.