Shaders manipulate pixels and have access to the depth so you can do 3d lighting stuff already. Couldn't you already do 3d water similar to the 2d water shader?
Or maybe you mean vertex shaders? Like what mesh distorts do but run in a shader? Since construct mostly just draws quads I guess moving the corners around isn't too interesting at this point.
I guess it could be more powerful if we were able to provide more data to shaders besides just number uniforms. For example: arrays, additional images, matrices and vectors. But that all may be out of the scope of what construct wants to provide.