There was another thread related to this idea and I had written some comments then.
I felt there was a place and time when more than technical skills should become part of the promotion process. I related that in the context of what I felt Aikido was about as far as what aspect of character was the key point of Aikido.
Since then I have had a very interesting convversation on this same topic with one of my former Sensei. He added to the equation some good ideas which are applicable to all Martial Arts not just Aikido.
Regardless if you think Aikido techniques are "deadly" or not students are being taught techniques which can hurt someone very badly.
Consequently at some point a Sensei has to ask themselves is the person going to be a good responsible individual. You do not want to promote or even keep teaching someone who will use their learning irresponsibly.
To exagerate the point, a Sensei would not even teach a person who comes to them and says I want to learn Aikido so I can be a better mugger. You would not give a gun to someone who will rob a bank or even just be careless with it.
The other point I liked is that for our purposes it is not likely going to happen that you promote someone because they demonstrated their charachter rather you would more likely fail to promote someone because they lack adequate standards of character.
As someone else mentioned so far it seems like the vast majority of Aikido students Ihave met seem to have good values. I wonder if that is unique to Aikido?