Custom sounds would be amazing in forge for more than one reason. One reason would be that some have made maps and they want to add sound but they can’t find a good one that fits the map having custom sounds would help in that area. Having custom sounds would also allow for some pretty amazing maps especially for horror maps or if you really want a realistic map and adding a gunfire custom sound to the map makes it better in a lot of ways.
I completely agree this sounds like a great idea that could be added very easily with an update! I might even put some fart sounds when people get killed lol. That would make the game very fun.