I think the main reason why we still don't have anything about goblins is because let's remember that they were hunted to near extinction, the few that are left are taking refuge in deep caverns (I imagine with a couple of human women that they managed to take to mate with them).
So I think that nowadays it wouldn't make much sense for a goblin to come out of nowhere and say "Today I'm a goblin and I come to attack because I want to fuck human women" because that would set off everyone's alarms and they would go to finish once and for all with the goblins.
I agree that maybe, at some point during the second or third phase of the village corruption, we will see the goblins in action again, although it's still not clear to me how Inatari plans to use them.
If in the end the conspiracy theory that the antagonists are goblins disguised as humans, then it would make a little more sense to me to see Yui, Marin and the rest having sex with the goblins.
Although now that I think about it, what if the goblins are for one of the endings of the game, like Dukall the antagonists want to use them for something, but the goblins betray them and finish them off to keep the power, the women and enslave the remaining men?