I think the Rooney Rule is working fine. The goal was to get more exposure and practice for minority candidates, eventually leading to their hire. To that end, it's been successful.
The issue is the talent pool available to become head coaches. If you look at the coordinators and hot college coaches, there just aren't a lot of minorities. The NFL would be wise to focus its time on helping minorities in position coaches grow into really good coordinators, then helping to promote those coordinators as head coaching candidates.
It will take years to be successful, but that's the most likely plan to long-term success I think.