The key element in the CPU market space is volumen. Volume lowers the cost of manufacturing and allows you to spend much more money on R&D as it is amortised over more devices. While all the big RISC manufacturers had in principle better architectures than Intel, in the 90ies Intel would kill them one by one due to the insane volumes of the PC market. Only on the server PowerPC and Sparc would survive. This is what forced the PowerPC to Intel transition, Apple had litte choices. I always keep wondering what the outcome would have been, if one of the large RISC platforms would have been made available in more consumer level products, e.g. offering an ATX motherboard for running Linux. Volumes would have been much larger.

Another big factor for Intel was, that, financed by their huge cash flow, they had the most advanced fabs, so competitors often were 1-2 generations behind in the available processes.

But now a few things have changed. First of all, Intel got stuck with their 10nm process, so they are no longer the manufacturing lead. But most importantly, TSMC would pull ahead of Intel and offer their services to everyone in the market. For the first time, AMD had a manufacturing advantage vs. Intel.

And the iPhone happened. Given Apple an almost endless supply of money and a huge volume. Over many years, Apple built up a leading chip-design team. This already paid off big with the iPhone, having by far the most powerful CPUs in the mobile space. This also gave Apple a clear insight into the advantages of really owning the whole platform. Designing software and the cpus together.

Offering desktop-class CPUs is of course a large additional investment - so it is not a trivial step. But if Apple is willing to do it, it should be very interesting and would give hope that they have ambitious plans with the Mac, as it only makes sense if they really push the platform.