I'd like to see dependent texture reads implemented in hw and accessible from OpenGL.
I don't know if anything like this is planned but Carmack has talked a little about it. Like you use (red, green) from the previous texture pass as texture coordinates in the next texture pass, or (red,green,blue) for 3d textures. This way you could implement almost any function you'd like. Sure, it'll be a little slow (very non-linear texture memory reads), but very useful.