If Apple really moves to custom chips in Macs, it's going to be about one thing only: independence. Apple wants to control the entire stack; and relying on a single vendor is too big of a risk.

It's not a question of price; it's about getting the chips they need.

Intel has missed a lot of targets in recent years, and (according to rumors) more than one recent Mac model has been delayed because Intel did not have the next chip generation ready in time.

Current Macbook Pros max out at 16GB RAM because the Intel chips don't support LPDDR4 RAM.

On iOS, Apple can control everything. They can plan ahead, and know that in 3 years they'll have the chips they need.

On the Mac side, they can only hope that Intel doesn't delay their roadmap longer than usual.

(The story about Marcipan (a shared iOS / macOS UI framework) seems unrelated to the chip issue. Sounds like they included it in this article only to make it look a bit more substantial. There is already a lot of shared code between macOS and iOS, and the CPU architecture isn't holding anything back in that regard.)