The article says that 28nm will dominate for another decade, even though 14nm fabs exist. Having to use extreme ultraviolet (really soft X-rays) for lithography runs costs way up. EUV "light sources" are insanely complex, involving heating falling droplets of metal to plasma levels with lasers. It's amazing that works as a production technology. The equipment looks like something from a high energy physics lab.
It's interesting that we hit the limit of photons before the limits of atoms or electrons.
Another problem with all this downsizing is electromigration. Every once in a while, an atom gets pulled out of position by the electric field across a gap. Higher temperatures make it worse. Narrower wires make it more of a problem. This is now a major reason ICs wear out in use.
Getting rid of the heat is another problem. High performance CPUs are already cooling-limited. This is also why 3D IC schemes aren't too useful for active components like CPUs. Getting heat out of the middle of the stack is hard. Memory can be stacked, if it's not used too hard.
There's no problem making lots of CPUs on a chip, if the application can use them. Things look better server-side; you can use vast numbers of CPUs in a server farm, but it's hard to see what 20 or 100 CPUs would do for a laptop.
Drastically different architectures may help on specialized problems. GPUs have turned out to be more generally useful than expected. There will probably be "deep learning" ICs; that's a problem where the basic operation is simple and there's massive parallelism.
For ordinary CPU power per CPU, we're close to done.