I think if embrasures were ever added to the base game, they'd have to have a smaller cone of visibility. I've used this mod last alpha and it does make the game a little too easy.

I'm no native speaker. Cone is the word I actually ment.

Yes, they give quite a too big advantage, but honestly I don't want to miss them when the next human-hunting pack comes along.
Against animals this is a fair strategy imo because they aren't as smart (although they could be smart enough to stay away but well, AI and stuff...). But when a tribe raid is just standing in front of them and let themselfs get slaughtered it feels kind bad.

I'd also be willing to do some coding myself (I have decent C and C# experience), altough I don't really now yet how RimWorld and it's mods actually work. Also I am in my exam phase so there really isn't that much time to do stuff like that.

But this mod shouldn't even to something to the AI. Hence drawbacks for using these are the best option.
Them acting as vents would be one idea. This does at least affect extrem temperature enviroments. So they can't shoot from well heated(/cooled) room all day long.

I'd definitely want to use these just for animal packs. 25 boomrats showing up is just OP in my mind. If I get my guys inside I need them to have the ability to fight back.

All this mod needs is for the AI to be able to shoot back through them like you can. I have had a few instances where they did indeed shoot back at me, but it was short lived. Currently it looks like its been updates so that enemies can pass through them which just makes them like sandbags. The idea of embrasures for me was to compensate for the inability to have walls you can get on top of and shoot down at enemies from cover.

I think the real problem isn't with the mechanics as much as it is with the enemy AI. Since AI is prone to charge doors/lower defenses behind walls you can place them pretty easily to shoot upon the enemeis as they try to breech. Also, the AI doesn't react as if there are holes in the wall which can be shot from -- they'll just run right up to it, and then start running away the moment you shoot them, but since they are wounded it actually makes it even easier to kill a few of them to make people run off.

There'd have to be some kind of breeching/avoidance mechanic for balance, I think. (Of course, if the enemy could mitigate these entirely, then what would the point be of building them into a base? Getting a fully defensible base is hard, but once it's up it should be difficult for people to attack too)

They could even set up shop outside of the base and begin building a mortar or something, perhaps if the raiding party is from a faction which has done this a few times and plans ahead by bringing muffalo along for the attack.

typically a castle was meant to be a self contained entity. To "balance" this would be difficult as really it was used by archers to shoot with near impunity.

Apart from them to act like vents and reduced visibility maybe material type could come into play i.e. wood walls block line of sight but do not offer full cover from gunpowder based weaponry above a certain calibre as really anything maybe above .22 can penetrate wood.

This then makes it scarier in the early game as it prevents complete turtling with cheap materials, but the stone variants and the walls should have an increased material cost meaning setting up meaningful quarry production.

I like Calico's idea, and the limited cone of fire. Perhaps cheap materials in the vein of wood only stop small caliber fire/projectiles. Another option might be to provide (if this is possible, I'd have no idea) an aim bonus/the cover provided is nullified when firing on the target in the embrasure with particular weapons, eg sniper, grenade at close proximity? Perhaps particularly small creatures could crawl/fly through, as well.

Is there a way to stop the hole from venting tempurature? Maybe even a toggle for it?

The only way you would do that in real life would be to have a sash window. in this mod, not as far as i am aware

limited cone of fire/visibility is brilliant

@Etznab I'm developing the Brazilian Portuguese translation of some mods, including this one here. Are you interested in including in your project?

I would recommend for balance purposes make the time to construct higher than a wall (You have to cut out the embrasure hole or build around it), make sure that bad guys can still shot at you through them (in my experience they can, I even lost a dude to a grenade tossed in through one RIP Rook, you will be missed) but I would also increase the cover effectiveness. Maybe also have it require research, but these were used in the Middle Ages so any industrial civilization is going to learn to use them quickly. I think an AI behavior tweak could also be helpful, but I don't know if that is something you can do in one of these mods. Certainly melees couldn't slice through it, but they could mine it! And enemy tribals could totally fire arrows into it. Anyways sorry for the three year late comment guess