It is quite obvious that the future CPU will have an increasing number of Cores, and most of the evolution of future CPU will be based on thinner engraving to pack even more Core/die. One on the first problem to rise with massively multicore CPU will be the interconnection of cores in order to get the most from the raw power, and make them working together optimally. To reach such goal, Cores have to be massively interconnected, as well as communicate with shared cache memory or via limiting system bus. Higher number of Core will make interconnections even more complicated.
IBM is currently working on a solution:
The strategy is to make Core communicate via laser. This is becoming possible with the nano technology allowing miniaturizing laser modulator. Even if this project is still in labs, it illustrates massively multi Core CPUs found in supercomputer might be interconnected in the future.
