I think it's hard to say at this point beyond the fact that is certainly isn't helping it.
The more proprietary APIs pushed the less likely someone is going to use OpenGL (DirectX is a great example). Apple doing this now basically means that a new game dev working on iOS and Windows likely won't even get to know OpenGL.
It's good to have a great performance, but if every vendor tries to implement its own stack for doing graphics, eventually OpenGL's development maybe slows down.
Probably, graphics programming might get fragmented by OS/Hardware vendors
The more proprietary APIs pushed the less likely someone is going to use OpenGL (DirectX is a great example). Apple doing this now basically means that a new game dev working on iOS and Windows likely won't even get to know OpenGL.