Why do you even want splitscreen? It's a game that require mouse+keyboard for proper play right now. Not really suited for a "couch experience" anyway. And why not just using two monitors with two PCs? You can still sit next to each other...
That is the thing. For instance, Serious Sam used shared keys on the keyboard for two people to use and even then, it was a clunky experience (and if you read their development history, they were always shooting for bringing the franchise to consoles). Most of the earlier day PC games that had CoOp either applied similar impractical play inputs or were a hot seat style of play.
Point is, anyone seriously attempting to entertain this is either trolling or being silly.
