Cpt. Praxius is already working on the German "egg" grenade, and he once mentioned that he might take a crack at a flamethrower sometime.
The important thing with the flamethrower is that it isn't added to Apartments or Granary. In any other map I can think of off the top of my head (I'm thinking Barracks, Sparta, Fallen Fighters) there's enough open area that you can pick them off. They'll probably be clumsy to carry I guess, and depending on the facts a good shot could take it out and all of his friends (although I'm not sure given the fact that I keep getting told they can't really explode after someone tells me they can). On Apartments however, especially if the fight happens in the buildings just after A/B, it would just be a joke. Granary has the same problem; while it would be fun during A through C, once inside they would just own up the joint, which is a shame given that Granary is exactly the type of scenario flames would be used for in real life.
Of course, when I say they wouldn't work in those maps I'm imagining players spamming flames pretty constantly, though there might be a way to mitigate that using real-world constraints. Maybe in the stairs it would be too close for safety of the operator. Plus there's the risk that the operator would just be some immature buffoon that burn his way through a building indiscriminately and racking up the teamkills.
Also, for the CoD doomsday sayers, there's only one per team. At least I hope that.