I always thought it's already true that if you start combat, you fully consent to the consequences of your own actions. Seems only fair that one with the intention to hurt must consent to be hurt.
I am truly amazed and would be a little disappointed if this is not already a rule, then good for pointing it out! :/
EDIT: Just took the time to read it all and I cannot agree more. RP becomes interesting when we rid ourselves of the childishness of not accepting the consequences of the actions anyone decide for their character to do. I hope we will get to see this implemented or at least get a chance for the playerbase to vote for it. The very fact that people are forced to take responsibility for their actions will make it SO much easier. It's like it would solve so much OOC drama cause you won't have the ability to whine, cause doing what you do equals getting back what you do. Damn fine reforms if you ask me.
5. Players may refuse to consent to character death if they believe that the roleplay basis for it is illegitimate. This includes, but is not strictly limited to: metagaming involved with the circumstance of the violence, powergaming in the violent circumstance itself, and OOC motivation leading to the altercation (spontaneous murder sprees, revenge for an alt's friend, etc).
-Escalation of violence may lead to a situation where attempting to kill the other party out of self defense is reasonable. To avoid confusion of who consents and who doesn't, it's always a good idea to discuss intended outcomes before a fight starts, which are considered binding (to original participants and any that join) unless re-negotiated by the original parties.