The ultra mobile and low voltage market
will have to eventually go dual or multi core. Shrinking the
transistors will last as long as the oil reserves, if even that long, and after we
come down to the size of a single atom, we won't be shrinking any more.
In that scenario you reinvent the core with a multi, dual, quad or more cores as you simply cannot make your gate any smaller.
As the ultra mobile and mobile market in general is all about heat dissipation and power efficiency, the ultimate goal is to have the high performance per watt. You want to render a 3D image on a 16 core CPU that will use 1 W, that would be the holly grail but it is highly unlikely that this will happen in the next few years.