While the idea may be interesting I think that it would change the meta too much and it would be too difficult to balance.
Which is exactly what many folks want. They want new weapons and new combinations. The same old loadouts forever get boring.
1.3 changed it some. The cqc game was altered enough where I think we should be seeing a resurgence of some flame based combat, which is good. Also the mines are adding another factor to deal with. This has returned some usefulness back to the gunner class.
The long range game is still being ran by merc/jack. Adding another standard mount weapon won't really change that. But medium mount weapon, that is where possibilities like torpedoes come in. Balancing wouldn't be as bad as you'd think. It would come down to speed, arming time, and power of the weapon just like any other weapon. The only other factor is combinations of the weapon on things like galleons. Jack/Torp combo could potentially be the most devastating combination ever unleashed in the game. But, with slow firing, reload, and potential for the torpedoes to be intercepted...there is the potential for countering it. Not to mention if the opposing team ran their own torpedo boat. The Jack/Torp would have to stay more mobile to be effective since the galleons move so slow that if they sat still firing, there would be the chance enemy torps would tear them up should they miss one, or if they got flanked by the torpedo boat.
That would be something, a light sniper boat drawing attention and fire to get a target spot to allow a fast Torpfish the chance to get in enough range to fire torps from a blind side. All the time using the bait boat as a spotter so the Torpfish could shoot from cover. How about that for your sniping meta!