I read the beginning. There's no reason to be looking for alternatives to tradition because the tradition works just fine and it's exactly what the pax want to see.
At every company I've worked at (3 different pax airlines) the FO was responsible for a few short items on the evac check, and then he ran back to deal with the evacuation. The Captain followed after he was done and took charge. The FAs are there to lead the initial evacuation, but the Captain is always ultimately in command of the situation.
At a station, the rampers, agents, etc... know who their supervisors are because they work with them on a daily basis and report directly to them. Major carriers (and even large regionals) have thousands of Captains. Without the identifying rank markings, no one would have a clue who the Captain was.
We're not always sitting in our seats. We could be greeting pax, standing at the gate counter on the phone with dispatch, etc...
It's a concern, but it doesn't trump all the other factors. All things being considered, it simply doesn't make sense to have pilots dressed as average Joes.
When pilots walk up to the gate, the pax are measuring you up and developing an impression of you. Make no mistake about it, your professionalism is judged by the pax in a split second based on your initial appearance to them. They may only see you for a few minutes before and after the flight, but in those few minutes you are a representative of the carrier and of the profession. You should have the traditional and professional appearance that the pax have come to expect.