Vulkan is really hard and is not really a "true" replacement for OpenGL. It's too low level, and not a good API for people making "games" to interact with. Sure, big engines and AAA games are definitely going to be implementing it, but it will always be alongside D3D and Metal.

But IMO Vulkan is way too much for most indies, small studios and solo developers to work with. I doubt we'll see many games targeting Vulkan as "the" multi-platform API like we've seen with OpenGL in the last 15 years. Anyone having to target Vulkan will have to use Unreal/Unity3D. Or maybe someone will develop a wrapper that converts OpenGL calls into Vulkan calls.

Honestly I see Vulkan as akin to regulatory capture. It will only enrich the big players by forcing small companies to use big engines.

EDIT: To give a concrete example, we (part time indie team) have an unfinished renderer in Vulkan, and it's already almost 5x larger than the other (finished) ones. To use Vulkan effectively, even on small games means you need a substantially large abstraction layer. Sure, it doesn't matter on AAA or for commercial engines, but not everyone is on such large projects.