Epic Games has just bought tech that will enable this feature

Epic Games has just bought tech from a company called Hyprsense. They specialise in creating tech that allows one to add facial expressions to in-game characters. The idea is that Fortnite will use this technology so that players can use webcams to control facial expressions of characters. This will lead to a much more submersive gaming experience. These features are still being developed and have not been rolled out just yet.