There are 2 fallacies here in this thread.
1. Arm chips being superior to intel core chips as far as performance goes.
2. Cellphone chips being considered in the same type as computer chips.
When you realise why these assumptions are false starters, please reconsider why Apple should cripple their computers even further than the Macbook Retina toys are already.
Then consider what does Apple have to gain from losing it's compatibility with existing OS X and MacOS software.
Then consider why should Apple restrict the possibilities of performance, and have the worst of both Mac and iOS in a device that will not be able to cut the mustard as far as performing worse than previous models, and for a higher price.
Then feel free to make snarky comments about the world renowned cheapskates at Samsung who are noted for making flammable washing machines, exploding galaxy note 7s and other junk of even less quality than the iPhone 3GS ?
1. No one ever insinuated this. No one is talking about putting a 5W A9 chip on a 15" rMBP. Do you know what Apple can do with a 50W ARM chip? No one does. All we know is that Apple is very close to offer superior performance/Watt on the CPU and GPU department.
2. Again, you are the only person saying that.
When you realize that no one is asking for Apple to put iPhone chips on Macs, you will see how hilariously out of touch you are with this thread.
Losing compatibility with current macOS software might be worth it if the right tools are ready and the (in theory) advantages like superior performance, superior power management, liberty to design their own products without relying on intel, rewrite the OS are all possible. If this happens, it makes sense. If not, it doesn't.
The point is:
ARM powers everything from watches to servers. If Apple can kick Intel's and everybody else on chips designed for watches, phones and tablets, what would happen if you said:
"Apple, build a chip for a 15" rMBP or an iMac". We don't know. You don't know. All we know is that they are better than intel on all segments they compete.