A Resident Evil Revelations 2 / Biohazard Revelations 2 Steam Community Group Announcement offers an "update on local split-screen coop" (thanks GameInformer). Capcom apologizes for promising local split-screen co-op for the PC edition, explaining the reason this is not included is because it was never planned as part of the PC release, and shouldn't have been part of its description. They say they are looking into potential solutions:

We apologize to our Resident Evil Revelations 2 PC players who purchased the game and expected to have local co-op as a feature. The feature wasn’t intended for this version and that caveat was mistakenly omitted from the product description on the Steam page earlier, and then included as soon as we were made aware. This was an unintentional error and again, we apologize for the confusion this may have caused.

We are currently looking into the matter and potential solutions and we hope to have new information to share very soon, so please stay tuned. Thank you for your patience and understanding.