Rejoice everybody! Though a plucky modder actually managed to beat them to it, Capcom has finally added local co-op to the PC version of Resident Evil: Revelations 2.
Revelations 2 supports split-screen local co-op in both campaign and raid mode, and though the update containing the fix is only available in beta form right now, everyone can download it.
Given that it was this easy to mod in, it begs the question of why Capcom removed the feature in the first place. The developers do warn players that "this option may not be 100% polished", and you might have to limit the framerate and enable V-sync to fix some stuttering issues.
Still, at least Capcom's attempting to atone for the pretty shoddy way it revealed the lack of co-op; a small disclaimer was added to the game's Steam page a few hours before launch, which wasn't really sufficient considering plenty of players had already splashed out the cash for a pre-order. Refunds for unsatisfied customers are apparently available through Steam, so it might be worth contacting Steam support if you want your money back.