Server-side rendering still makes sense, because the server (the user's laptop or phone) has its own dedicated GPU, and the client (racked in a shared datacenter) likely doesn't. So I think we'll keep seeing browser frontends for everything.
Yeah, but that kind of workload isn't really X, OpenGL and Vulkan are designed in a way that X isn't necessarily part of the story, and CUDA, SYSCL even less.