never say never. if there's a topic where there wouldn't be reason for off-the-record stuff, we'd be happy to stream it. it's hard to think of something right now, possibly hiring.
I think it would be hard to predict what topic people wouldn't be candid about.
But more importantly, people change their behaviour when they're being recorded. So many speakers have been 'unprofessional' (for want of a better term) in a way that they wouldn't have been if they were recorded.
The only solution I can think of is to record them without telling them, edit out the 'candid' bits, and ask them afterwards if it could be shown publicly. But that might ruin it for later speakers, since they'd know it could happen.