Golden Forest image - Enderal mod for Elder Scrolls V: Skyrim

No as the Skyrim egine is hard pressed with with firearms, the canons are there to mark the place of a great fight in the past between Thalgard and the Order ;-)

Enderal doesn't use any DLC, hence no crossbow (though SureAI went as far as animating waves, because without Dragonborn, there were none of those ;-))

Also the crossbow would be a bad starting point, as the loaded projectiles are essentially arrows and move closely like arrows shot from bows (both are flying in a parabola, the arrow has just a higher speed if shot from the crossbow, hence it gives the illusion of shooting straight ;-)).
Bullets fly completely different and if you would want to do it at least semirealistic the bulletspread would have to be enormous and random. This would need complicated scripts for calculating the trajectory and then letting the bullet fly exactly that path.

Can you imagine the nightmare such a weapon would pose if you try to limit the amount of scripts so that Enderal runs smooth without CTDs and doesn't become another Nehrim on the performance side? ^^

1. yep it would be - you would put sth you need to pay for for free into the public - that is always illegal

2. bullets habe a much greater spin and way less weight than arrows have, hence their trajectory is affected mostly by the coriolis effect rather than by gravity - a bullet rather starts spinning in a circle with the radius of 0,5 m than dropping to the ground due to gravity ;-)

3. Luck based shooting systems (short accuracy ;-)) like e. g. in Risen 2+3 or Fallout are always a pain in the *** - they are the easy way out and do in no way reward player skill
Also you would have the problem of having 2 shooting systems in the game at the same time - once animated arrows for bows and once possibility-based calculation of bullet hits --> your engine will not thank you for that.

The history of firearms as you described started in modern age only ;-)
In the first half of the 15th century to be precise, which is also when the modern age began. The arquebus was among the first weapons with a trigger.
And for those we have exactly the problem I pointed out in my second post here - it took until the beginning of the 16th century until you had the rifled barrel. Adding to that you have as you said casted metal bullets which were in no way or form even.
Hence the bulletspread wasn't just huge but also completely random. Firefights of that time were won by the pure number of soldiers shooting, not because of an precise aim.
Hence making it even semirealistic would need you randomnize the bullet path in each shot, effectivly making it an useless weapon the game unless standing right in front of the enemy and then you could also just hit him with your sword ^^

You really like firearms, don't you? :P

"Also there's a lot of old games that randomise weapon spread and have no issues with performance, and mod team would use same mechanics to all ranged weapons, but bow would have set 0 spread radius. "

Now you miss the point - it is just that Skyrim's creation engine cannot support firearms as easy as you make it out to be.
Such old games had engines which allowed for that from the beginning - Skyrim's does not and without the source code changing the engine is only possible with scripts which massively lower performance - just as an example: if you could play Skyrim at lowest settings with just 30 fps, you will have 15 or even less in Enderal with the same settings.

In general you will have to turn back your graphic option one magnetude if you wanna play it fluidly.

That is just how demanding Enderal is for Skyrim's engine, which is nothing other than a heavily modified Gamebryo engine Bethesda uses since Morrowind...(Fallout 4 btw uses the same engine, modified so that it supports firearms - as they have the source code and more than 50 developers such a thing is possible)

Now add a big amount of scripts for firearms and your game will start to give out CTDs left and right - the disadvantages completely outweight the rather small benefit of a new class of weapons.

Well yeah it isn't in there, that would be code trash as it isn't used in Skyrim and such should be avoided as much as possible as it can affect the stability and performance of the game ;-)

" I'm just proposing firearms as it would be a good gameplay addon and it gives more choice for player in playstyle. "

Yeah I know and I think similar but even if it would be possible - balancing it would take time - much of it - and I don't think that would be the kind of thing one should put much time into when seeing all the work left still ;-)