We can and should trust everyone on a team with any role when the conditions and limits of their contribution in that role are clear to them. The principle of fluid roles tells us to prioritize trust building within our teams so that everyone grows in their ability to recognize opportunities as they reveal themselves and to contribute in whatever way fits that moment. That means serve in whatever role is most appropriate for the team and that moment.
This is a great point from your generalist article. I think this is the hardest thing to get around in the corporate environment ... people often "specialize" themselves right out of a generalist role by circumstance.