The Steam Store page for Resident Evil Revelations 2 [official site] has listed offline co-op as a feature since preorders began and continues to do so at the time of writing. But the game, now released, doesn't support local co-op and, according to a statement Capcom have made to VgG24/7, it probably never will.
The PC version of Resident Evil Revelations 2 supports a variety of customisable visual settings and resolutions. The decision to prioritise a single local screen was made to ensure a stable user experience across a variety of different PC settings and devices.
PCs have too many graphics to support splitscreen.
A footnote has been added to the Steam page:
"2. The PC version does not support offline co-op play in the Campaign or Raid Mode."
Considering that those are the only modes in the game (unless there's another mode hiding from me), it seems odd to mention offline co-op on the page at all. And yet:
The second part of Capcom's statement appears to put the kibosh on any possible future integration of offline co-op.
Raid mode will support online co-op shortly after launch when a free patch is available for players to download which adds this feature, but the main campaign on PC will only be available to play in single local screen.
Capcom are probably attempting to have the Store page updated (again) as soon as possible but anyone who preordered hoping to play with a chum is plumb out of luck. It's a twist on the usual preorder bonuses, being a form of preorder penalty, and there's no trace of an apology in Capcom's statement. Granted, this may be a case of the left hand not communicating with the right hand, but when either hand is taking money from people it seems reasonable to expect the basic facts to be correct.