It seems so obvious that I'm surprised no RPG - to my knowledge at least - has done that yet.
Weeeelll technically Pathfinder has always had an in-game use for the Intimidate skill (called Demoralize, it can potentially inflict a status effect on the enemy). And you can actually use Diplomacy in combat, too, though it only changes enemies from Hostile to Unfriendly, so it's not a guaranteed win or anything.
The Kingmaker CRPG packages these skills together and includes the Demoralize ability. And actually the Demoralize mechanic is part of one of the strongest feats in the game.
So yeah. We already got a game that does that.