It would be awesome, it would function like the game and the movie, one player starts infected and after a while they become a Thing, The thing team would have a tier based system where you unlock new classes through kills.
Infector? (Dog Thing):
Flamethrower. (Kills T2 to 4 without allowing them to regenerate.)
MG. (Kills T1 and weakens higher tiers.)
Rockets. (Starts fires. Kills T5.)
Grenades. (Same as rockets but wont kill T5.)
Pistol. (See MG.)
Atleast TEN. (Or make NPCS of the infected.)
Ill update it more in a minute.