Some projects need a Benevolent Dictator. Linux and Python are two good examples. Imagine what these projects would be like if Linus Torvalds or Guido van Rossum were replaced by committees!! Email Authentication has now demonstrated, beyond reasonable doubt, that it cannot succeed with everyone pulling in different directions. Someone needs to step up and assume the role of BD.
A BD needs to make wise decisions, even if they are unpopular. Contrary to what is implied by the name, the BD's power is strictly limited by the consent of a volunteer community. Those who complain the loudest often stay with the project in spite of their complaints. They do so because they realize the alternative is an incoherent mess.
The first thing an email BD should do is break the deadlock preventing deployment of the currently developed methods. This should be done not by picking one as the winner, but by providing a neutral standard or platform within which all methods can operate. A wise BD will figure out the minimum things that need to be standardized, and not include any items that will truly inhibit one of the methods. I say truly, because it will be necessary to listen to the screaming of tortured zealots and distinguish between "hate it" and "can't live with it".
BDs usually start with a small community, and stay in power as the project grows. The Email Authentication community is already huge and split into warring factions. A little bit of money can overcome that problem, as demonstrated by Mark Shuttleworth in bringing order out of the chaos of Debian. Compared to the cost of email abuse, the cost of funding a few well-chosen projects is minuscule. Money isn't everything, however. Even the richest corporation cannot assume the role of BD if the community sees it as unfair.
Just my $0.02 for anyone considering assuming the role of BD.