> Who knows what kind of crazy performance differences/bugs there are between ARM and x86_64.

A lot of code for demanding applications is often enhanced with SSE/AVX and JIT recompilation techniques. Those are inherently unportable, and I'm not sure how many developers will be willing or able to port that code over to Neon and AArch64, especially for a small 2-4% of the market.

Even if they do, it's quite a cognitive burden to have master and maintain two separate SIMD and recompilation implementations for the same applications.

This will probably further drive high-end gaming away from Macs, on the heels of OpenGL deprecation and the Mac-only Metal API. Combined with Cocoa and Swift, I imagine we'll end up seeing less and less applications that run natively on both Macs and Windows/Linux after the move.