Dual Wielding weapons that are not light weapons, and have high reload time is so bad it is basically a non-option.
The Damage output of the class suffers because of three things:
-base damage being so low
-drought of feat and ability based damage enhancement
-a low "rate of attack" due to high reload time, capacity, and cost prohibition of keeping additional pre-loaded weapons.
Play-test friendly Options for solving these problems are:
-additional feat or class ability "damage boosters"
-opening up some of the archery or crossbow feats for use with firearms.
-offering a "cost" chart based on how common firearms are in a region, possibly.
-Possibly, give the class a firearm repair ability, and say any firearm with the "broken" status buys/sells at half cost. This helps firearm focused characters purchase things at a lower rate.
Personally, i favor enhancing "damage/payoff" per shot over increasing the rate of fire. While many people dont like the called-shot-like mechanic, i think that the ability to gain some utility from each shot is a viable alternative from additional damage. (Status effects, or eve combat maneuvers at a range)
However, increasing the rate of fire by lowering reload time should be an option, over damage or utility. It would put it more in line with the other weapons, but basically demand that the weapons no longer be ranged touch.
Personally, i treat firearms as crossbows for ALL PURPOSES, except that i simply house-ruled that there is an equivalent firearm feat for every crossbow feat. Longarms are equivalent to heavy crossbows, and One handed firearms are like light crossbows. To dual wield pistols, i required something similar to monkey grip, since they are flipping hand cannons, not the light pistols of today.
Its safe to assume that there will be firearm using Archetypes for other classes in the future, and establishing a sweeping rule like this would give a lot of mileage toward directing future supplements.
(for the record, i think rogues, rangers, bards, alchemists and inquisitors need a grit-archetype.)