It is a very interesting concept. I am going to do some math here though, lets say for example we have a server with 20 people in it. 15 of those 20 are zombies and the 5 remaining survivors are doing very well. Now for the purpose of the example lets also say that each zombies dies 10 times during the course of the game. That is about 150 collective zombie deaths. Now because each zombie only gets a chance to respawn as survivor every 10 times they die, we will divide 150 by 10. This gives us 15, and because they only get a 20% chance of becoming a survivor every 10 deaths. 20% of 15 is 3. That means over the course of this game 3 people get to respawn as survivor with speedo and a 500 damage knife. Sure, this is a great occurrence for these 3 zombies (now survivors) however, now there are 8 survivors instead of 5, and now there are only 12 zombies to kill them. I don't think this is a bad idea, I just think it might start a cycle where, instead of it being harder for the survivors to survive as the game goes on, it is now gets harder and harder for the zombies, and easier for the survivors. All of this does not even account for the higher chance of respawning as survivor the more times you kill a survivor as a zombie. Sorry for all the math, just hope I could point something out.