Why would guns be gamebreaking, and where is the limit that marks an item as a complete anachronism? Also, on what scale do you measure anachronism? If you measure it on the time scale, a kevlar armor is a less grave anachronism than a classical era roman armor. If you measure it on another scale, please explain which and provide examples of how some of the currently implemented items are ranked on it.
Guns would completely reformat gameplay. Even basic 1-shot guns shoot projectiles faster than one could possibly dodge, they're often armour piercing, and are small enough that a couple can be carried at a time (along with a bucket of ammunition). Crossbows are armour piercing, yes, require little skill for short-medium range shooting, yes, but they don't fire faster than one can move and they're quite bulky too.
As for the scale of anachronism I was considering context more than chronology. Kevlar is out of context, it seems, because it exists as a reaction to firearm technology. Roman gladii, on the other hand, are a reaction to frequent close combat fighting and a need for a reliable rudimentary close-range stabbing weapon. The concerns that prompted the use of gladii by the Romans are very similar to other cRPG gear. The huscarl shield, for example, could stop arrows from any distance and batter people too. This is almost identical to the purpose of the large Roman shields used in the later Republican era for forming anti-projectile formations and for battering Celts. It's also quite similar to the massive shields employed by Athenians in spear walls when they fought Philip of Macedon.
These are my perceived criteria for how the devs gauge which gear to include. Of course they may have a different system (and likely do), and of course this system becomes much more subjective on the periphery, but it doesn't seem massively incoherent to me. And, as I said, there doesn't seem to be a developer's manifesto laying about. This is probably the case for a number of reasons but one of them is likely so they're not tied down to anything in particular. In two years time it may be that there are guns in cRPG, and in four years time there are WWI-era tanks. Until then, though, players are free to make suggestions and argue for the inclusion of items into the game so long as they seem to fit the gameplay the devs are pursuing.
Remember that I said earlier that this was all based on the developer's own standard of reasonableness. I'm not sure what that is and, of course, propositions about what it could be^ are largely guesswork.
