I could suspect some class by Mage Hand Press could appear in D&DBeyond but the surprise arrives because there is no warning.
I guess the adventage of the 3PP classes in D&DB should be the free homemade subclasses. Even if theses hadn't got the right power balance enoughly refined other player with enough experience could publish his own "update patch".
Other point is the PC vs DM "arm race". For example the DM could say the cities have got a special magic area effect thanks the temples and when a firearm is shooted thanks divination magic the investigators can know where, when, the shooter and possible victim, and where is the fireram is now. Firearms couldn't work within certain magic areas. For example if a group of robbers who entered a bank during a robbery their guns couldn't be shoot, their canons would be blocked, and a minute later the bullets would be teletransported out. Only the gun by the security guard could shoot.
The castles and strongholds could enjoy some "wondrous architecture" (immobile magic item) that created a magic area where the gunpowder by attackers could work. (magitek firearms could work but they are more expensive and then the power balance shouldn't be broken so easily).
The automatic firearms may be too powerful for D&D standards but its complex mechanism make those too easy to be unusable thanks low-level magic, something style the gun jumming, or the barrel may be deformed by the heat. A "handcrafted" automatic firearm may be too expensive, or no not very much cheaper that magic wands. The automatic firearms "imported" from other wildspaces or industrial factories from Mechanus are too expensive because you have to pay the travel. Deities will not allow building of firearm factories.
What if a player wanted to create a biopunk crossbow with artificial muscles that allowed to reload itself? At least it would be quieter during stealth operations.
