Modders said they would do it and they followed through. Resident Evil Revelations 2 on PC now has split-screen, local co-op support. Capcom had originally stated that it was never intended for the PC release, even though the feature was being tested in the backend.
You can never fault Nintendo for not taking some risks with adding ridiculous elements of fun into their games. The Wii U exclusive Hyrule Warriors has a new bit of DLC on the way that takes the concept of flying the coop to a whole new level.