Vulkan is the immediate future of open graphics, and I see it taking the same path OpenGL did - becoming the defacto standard for 15-20 years, and then being supervised by something else that fits the newer technology of the time. Will it eventually go away? Sure, but for now that’s where all the features, support, and industry attention is going (and when it comes to fully utilizing the GPU and supporting multi core processors well, it’s miles beyond anything modern OpenGL can do).
No… Apple has already deprecated OpenGL on Mac/iOS devices in favor of its own Metal API (which is conceptually very similar to Vulkan - similar enough that MoltenVK allows you to run Vulkan code on Apple devices with little to no overhead). Sure, it will be quite some time before OpenGL code can’t run on a standard device, but as industry attention shifts towards Vulkan I don’t see the support issues with OpenGL getting any better, and they could easily become substantially worse. If nothing else, others tend to follow suite whenever Apple drops support (remember Flash?).
My take on this is that there’s no immediate need to frantically push a jME4 with Vulkan support, but this is where we should focus in the long term. Win, lose, or draw, Vulkan appears to be the future for high-performance graphics, and if we want jME to stay relevant and useful we need to keep up with the industry.