There is no guarantee that a phone-scale CPU can just become 4x faster by 4x'ing the power/TDP/die area. If it were that easy, Intel would already have done it (and no, the x86 architecture isn't so terribly inefficient that they are leaving triple-digit percentage improvements on the table).
What I expect we'll see are ARM chips that are power and performance competitive with x86 chips only for specific curated use cases. Apple will extract an advantage by putting custom hardware acceleration into them, to cater for those specific tasks. They will not be able to achieve general purpose performance improvements wildly beyond what Intel can already do.
This is how the current iDevices achieve their excellent performance and battery life. Not through raw general-purpose CPU horsepower, but by a finely tuned synergy between hardware and software. Apple are taking their desktop down the same route. This will be the ultimate competitive advantage for their own software - they will be able to move key software components into hardware, and make it look like magic. But as a developer, you won't be able to participate in this unless you target Apple-blessed hardware instructions/APIs. Your Python script isn't going to start running 4x faster unless you can convince Apple to implement its inner loop in custom silicon.
I have no doubt that Apple will be leaning hard into ASIC territory as they build out their new CPUs. The endgame? Every software function you need, baked into perfectly optimised silicon by the monovendor.