I've been hoping for some crazy thing like WebCL to happen. I know it's nuts but, imagine how useful that could be for things like scientific apps and engineering apps. Little climate sim in your browser :)

Yeah I know, this isn't what browser are meant to do :) But I've been looking a some algorithms for cuda and opencl to extract isosurfaces from volume data and, it could be cool to do so in a browser for medical imaging purposes.

Who needs C when javascript can do all that ;p

EDIT: In all seriousness, this could be really useful for game developers on mobile. This could help them get closer to native games in terms of performance.