This is a neat idea - but don't kid yourself: if players want to know what Gnoll stats are, the internet is a click away and the stats are there. Or if you're old school, nothing is preventing them from spending a few bucks to pick up whichever book has the information in question. Switching it off in game is going to have zero effect on players' abilities to get to the underlying info. There just isn't a 'fog of war' world available out there unless a DM completely home brews something. Which leads to an intriguing twist on the idea in this thread: granularity -- to allow DMs to set their campaigns up as they see fit. Perhaps in your world, there's no coming back from beyond the grave: Raise Dead, Resurrection, Reincarnation and the like don't exist. Or perhaps you think gnomes are ridiculous and shouldn't exist as player character options -- or at all. In a blackboard world, each rule, item, spell, weapon, etc. would have an on/off switch, default set to 'on' -- but that would allow a DM to customize as necessary and perhaps allow another feature to exist: modding. Pay a book-sized fee, and you can write up any rule, item, spell, weapon, etc. and turn it 'on' for your players. This is probably a fantasy and programming nightmare -- but it IS an interesting idea, no?