Starting as early as next year, software developers will be able to design a single application that works with a touchscreen or mouse and trackpad depending on whether it’s running on the iPhone and iPad operating system or on Mac hardware, according to people familiar with the matter.
The report is thin on details as to how this would work, so the floodgates have opened for speculation. Some have suggested that this means Macs are moving to ARM processors. I think this move, however, is entirely unrelated to the possibility of ARM-based Macs; a single app can contain multiple binaries, each compiled for a different processor. And such a transition would take years, anyway, just like the transition to Intel processors.
I think this is much more likely to be the outcome of a unified set of libraries and APIs that will be available on both platforms.