I've been thinking for a while about this
and how cool it was, then I added a little bit of Urban Dead into the idea.
Basicaly, fire seems to be an area into which nobody has given any consideration (although I don't know whether the team has discussed it or not) but I thought it might be worth looking into.
So, maybe a flaregun weapon would be a nice touch. As I said, my inspiration mainly came from the flaregun in Urban Dead, but flaming zombies have a serious appeal.
This is just a basic shape of an idea, in the hope that people will discuss, feel free to burn it to the ground (hah, I'm funny).