Well first of I'd like to say that the reason I'm personally interested in split-screen is that I have an irl friend interested in the game, unfornately due to my country's situation I'm unable to afford another computer, I'm leaving the country sometime soon and I probably won't see him in person again and it's disappointing that this feature exists already in console.
Other than that it's very possible, there's a Local Multiplayer section in Steam and the code already exists, why not add an input option menu? Like Player 1 is set to Keyboard + Mouse and Player 2 is set to gamepad.
I know this topic exists already, but bringing it again would show there's interest for the feature.