Is there any give to the rule on one protagonist? The very appeal to the fantasy characters I have in mind is that one's a Blood Knight and the other's a Paladin and they're dating. If not, I'm sure I'll come up with someone else. However, if you're into anecdotal evidence, I have played in a similar "Everyone GMs" freeform like this, where multiple protagonists were allowed, and it ran just fine. As long as there's good characters, and people can stay in those characters and keep their GM selves separate, it's a whale of a time. Of course, if you're trying to keep the adventuring party from becoming an adventuring army I could understand, but this is a large group roleplay, so that might end up happening regardless. 

I guess there is a litany of problems that come with multiple characters, though, since I guess they can be tough to differentiate in narration sometimes and maybe things get weird if they're in wildly different locations. But I won't argue with the rules or attempt to change your opinion. I get the sentiment behind that rule, and what you say  undoubtedly goes. All I can say is that I'm up for some awesomeness and definitely interested. ^.^