They're not much more impractical than Varric's fully automatic crossbow, or Sera being able to pull arrows out of Dorian's arse.
Pillars of Eternity has guns and they blend seamlessly into the setting, being harder hitting than bows and most crossbows but slower to fire. Don't see why Dragon Age couldn't do something similar. Of course, the limitation of ammo is handwaved away, but that's the same for every single projectile weapon in every single RPG, unless you're called Skyrim in which case the game throws arrows at you anyway and you can hold thousands without being incomodated in the slightest.
Ammunition wasn't even a consideration, to be honest. The reload speed simply renders it impractical for dedicated use for the chaotic-skirmish type of combat that is routine in Dragon Age. Users would fire the weapon when combat was initiated, and then switch to something else to engage the enemy. In this sense, it would be a tool that all classes could use.
Trying to implement firearms as a weapon specialization or making certain specs focus in them would bring on the balancing nightmare. Firearms would, predictably, out-damage bows shot-per-shot to make up for attack speed. This in itself isn't really realistic, but whatever. If we were being realistic, anyone would drop a musket in a hot minute when presented with something like Bianca. Overall, I think this method of using firearms can work for games like PoE and tabletop, but I can't see it functioning well in the real-time gameplay of Dragon Age.
Instead of clumsily trying to mimic the real-life progression of firearms, they could try to implement them in a way that actually makes sense with the current state of technology in Thedas. However, I don't think they would chronologically come about in time for the next game. Also, people would cry. After all, we'd literally be playing Call of Duty. Literally.