If this were implemented, I'd accept challenges for "blind" games, but not before I created or modified a deck for it specifically. Anything where you select a card from opponent's hand (Sphinx), something is discarded only if it exists (Corrosion cloud, Dragon slayer) or the effect is based on a number of something in both hands (Retribution, Divine intervention) would be effectively useless and undesirable. These are just examples that come to mind, far from a comprehensive list.
And New card flags should definitely be visible, both because certain cards rely on that knowledge and because, were this a game being played face-to-face at a table, you'd see what card was played. Of course, while the above-mentioned cards would be less useful, others like Trigger trap would be even more powerful.
I wonder whether the decks used for such a game mode would end up looking very similar with people relying on (and avoiding) the same manner of cards.