Totally agree Archon, though maybe that is slightly one reason not to have them as well I guess.
They wouldn't add much different to crossbows, a bit more power, a bit less accuracy, a longer reload time, totally useless in rain, 3 or even 4 slots once you include the gun, the powder and the shot.
Perhaps a random "misfire" chance that gets lower the more wpf you have just to add some historical accuracy.
I fully accept that a great many people in cRPG and M&B as a whole feel that firearms don't belong but they could be added in a way that was interesting and fair for those who did like them to no more effect than a current crossbow on those who dislike them.
It wouldn't be worth it though if it caused a major split, and resulted in "early medieval" and "late medieval" servers.