My "solution" to this (and I say solution because I agree that adding action group visibility to bread crumbs would still be a welcome feature) has been to make less use of action groups and more use of projects and folders. Rather than having a project with a bunch of action groups, I'll have a folder with a lot of contained, small projects. You miss out on some things with this though - setting flag status for an entire folder, due dates for an entire folder, etc. Adding some subset of "project" style meta-data to folders for inheritance purposes only would solve this.

I don't know if there's still interest in this, but I would love to have this feature added. When I process my inbox, I add items to projects, but then have to go to that project to move the action to the right action group. Maybe in 2.0?