This is already happening to some extent in the high-end and has arguably already happened in large-tablets (upgrade cycles elongating). Smartphone units are still showing high growth since the market isn't saturated yet - especially in the low-end where many don't have a smartphone yet.
Also witness how smartphones are becoming more like fashion accessories vs. utilitarian devices to spur upgrades.
There is still replacement demand. There is still innovation where new semiconductors provide new capability. Semiconductors in-aggregate are a mature industry (cyclical) that goes up and down with GDP. It's not a growth industry.
No. I'm saying that the PC market is over-served by CPU performance and i3-level performance is good-enough. Witness how folks are willing to trade CPU performance for mobility (Core-M vs. Core-i5/i7). Benchmarking the new Macbooks shows it's slower than 2-3 year old macbook airs, but it sells at a premium to macbook air.
Furthermore, Apple and others can differentiate from Intel with non-CPU features (comms, gpu, dsp etc.) and tighter hardware/software integration.