If you wish, you can start developing in Godot. While OpenGL is being deprecated, there will still be some sort of support. So even when Apple goes full-on Metal, I'm sure there will be a way for you to support your game.
With regards to the Vulkan renderer, it looks like that's a ways away. Vulkan will be the renderer in version 4.0 of the engine, and that may be, roughly, 6 months away. (Though note that the development of the engine has quickened in pace over the past year.)