Can confirm both of these - I've played multiple games against Kethek where the trigger reveals the opponent's entire library.
I'm currently in a game right now where my opponent has a Kethek in play, and the last four triggers they've declined to sacrifice a creature and still a (seemingly...
As a big Premodern fan, I would love official support for the format on MTGO. It's a fantastic format with a vibrant and growing community, and an official queue (and maybe leagues, as well) would only grow the format and introduce a ton of players to a card pool many are largely unfamiliar with.