When I was really active in rp, it was mostly journal-based. I'm only doing PSL right now because I don't have much choice and my friend doesn't want to do the journal thing anymore :D
The games I had been in weren't completely open, just to a point. They had a list of races but you could create your own and present it to the mods in your application and they would accept or deny it, or even sometimes will work with you if they want to see some changes. One game I was in on LiveJournal was completely free-for-all when it came to races. There's still the no god-modding rules and stuff, anything major like pregnancies or death had to be approved first. But I think something like that would be fine and would work. I have seen some games like that recently, but all of the ones I found had a rule that vampires couldn't reproduce, so that left me out.