Apple illustrates a segmentation rather than a convergence. Tablet, notebook, and workstation are breaking into distinct bands of performance. In their world a tablet is for a guy who wants a couple cores (with long battery life), notebooks are for people want a few cores (with moderate battery life) and workstations are for people want lots of cores (the electric bill be damned).
In the PC market there is more overlap, with pretty solid $700 minitowers, but again the minitowers imply you will pay for the electricity and performance with a cost in size and portability.
Long term ... sure maybe a 12 core tablet is possible, but that is really long term IMO.