For long spans of Mac OS X's history, Apple always shipped an incredibly old version of OpenGL. With Apple deprecating OpenGL, this isn't really anything new or interesting — that is, until the day Apple removes OpenGL, we will have the exact same situation we always had: a really old version of OpenGL.

In the mean time, people have already developed ways to run OpenGL code atop Metal. A lot of game developers have already started to move their code to either Metal or these OpenGL-compatible shims in order for compatibility with iOS, so a lot of the adoption has already begun.

I for one have never really felt or noticed the effects of poor OpenGL support on macOS, at all in the last 10 years.

Metal seems much more compelling anyway, the Apple lock-in notwithstanding (even that is not so bad considering you can still target 4 rather popular device categories with Metal.)

Just like console vendors.

In fact had Apple not chosen to go with OpenGL ES on iPhone back when they released it, OpenGL would be pretty meaningless nowadays.

The few people buying NeXTSTEP computers for graphics programming were doing it due to Renderman, not OpenGL.