Oh, you certainly can get the controller of sibling directives from the expandostore in the controller closure! Unless you're using certain versions of jQuery which are currently slightly broken (in combination with angular, such as v2.0.x), this does work and I have apps showcasing it.

But at any rate, this is a feature and it's going to be some time before it gets merged, if it gets merged at all. There are already tools available to do this stuff.