I talked to Jeff recently -- they're doing cool stuff with immens. AFAICT, Superconductor does a couple of things differently. First, it is DSLs for making new visualizations, not running analytics within ones they've prebuilt. Second, Immens uses server preprocessing -- we do not require it, and only use it to drop data loading from 5-10s to < 1s. The idea of a render cloud is great (others do this as well), so I've been chatting to Spark folks (http://spark-project.org/) about a backend to compile our DSL into real-time graph processing on the cloud. A shorter-term option may be to extend our CUDA/OpenCL backend to use new multi-GPU extensions.

RE:WebCL, WebCL is simply one of our compilation targets. We can also compile to multithreaded C++, JavaScript (naive or typed arrays), OpenCL, and CUDA as well. For the web space, I'm working on an accelerated alternative of (workers+asm.js)+WebGL, and going from WebCL to RiverTrail isn't too big of a leap.