I started working on the max breadcrumbs concept and perhaps I'm just having trouble wrapping my mind around  the recursion but I can't see an easy way to implement it. It seems the way its currently written parent admins can add to the breadcrumbs which could potentially add multiple items to the breadcrumbs and I'm not sure how we'd enforce this since its happening outside of the buildBreadcrumbs method in this admin class so a member variable for current count or a local variable would not be available.

I considered the routing bundle approach you linked where you get the candidates from the Url and that could work but if you dont use the parent buildBreadcrumb functions then it seems you have to duplicate the localization code inside of the base Admin::buildBreadcrumb method. If you use the parent buildBreadcrumb method you have the same issue stated above about being unable to control how many items they add to the breadcrumb.

I am somewhat inclined to say that a menu with enough recursion to cause a problem in the breadcrumbs would be an edge case (most websites sites out there do not have more than 6 levels of navigation).
  
I admit this may be an issue with my understanding of the recursion but relying on the parent::buildBreadcrumbs function seems to take the ability to control the total # of breadcrumbs added out of the hands of this method so if you have any ideas let me know.