Interesting theory. I wonder then what will happen when Macbooks start shipping with >A12 CPUs [1], will we see more ARM based servers then?
Sure it will take more than a few tenth of a percent of mac developers but it won't need total domination like x86 either. But just imagine if Apple really just switches its MacBook (not even the Air or Pro ones) to ARM64 that would already be millions of users. A lot of devs will at least try to compile their app for that platform for the first time. Quite some developers will be curious and get one just to test their software on it. I am pretty sure this is going to help the adoption of ARM64 way more than a slightly improved CPU or another experimental support by a cloud provider.
Personally I don't care too much about ARM64's success (although more competition would certainly be great), I am more rooting for RISC-V and I hope they follow a more developer-first strategy.
And if Apple switches pro line to arm, they’ll probably lose all non iOS/macOS developers. So, good luck to them then there.