If you can't go smaller, make more and/or build skyscrappers.
My prediction is that the next step will be 64,128, 256, 1024, 2048, 4096, 8192, 16384, 32768, .... cores on a single piece of silicon, keep the size small, to keep the power usage low and the switching speed high. Also small means less complex clocking, where the entire circuit is much much much smaller than a wavelength of the clock, and the clock level can be approximated as constant over an entire core.
Another option is to build the chips more in the Z direction. We use to have mostly single sided PCB's 40+ years ago (still used in PSU's), these days they are like 4-38 layers on PCB's. Each extra manufacturing step adds a risk of defects. What really needs to happen is new methods for defects to be repaired, tolerated or bypassed.