Amelia Bones:

"It also seems this Defense Professor gave a most stirring speech to his students, just before last Yule, castigating the previous generation for their disunity against the Death Eaters." The old witch looked up from the leather folder. "Madam Longbottom was rather taken with it, and insisted that I read the entire thing. The argument struck me as familiar, though I could not place it at the time. But then, of course, I had thought you dead."

So it's not totally clear from that if "Munroe" specifically proposed a Light Mark, or just made similar speeches advocating unity or what. But whatever the case, it seems that, while yes people were talking about him as the next Dumbledore, saying he could become the next Minster of Magic, etc., they were not uniting behind him to his satisfaction.