We used to do Townhalls and streams about the sorts of things you proposed. MANY of them can be found on YouTube that were relayed or uploaded there over the years. It can be a slightly-dated, but still somewhat relevant way to hear about some of the evolution and watch or listen to interviews with many witnesses, some of the past and some of the present. It's going to take some keyword hunting to find them at this point usually, but try YT searches for "hive" "hive witness interview", that sort of thing, but also look for steem, steem witness and variants of either hive or steem keyphrases. There's a ton of interesting stuff there :) Granted its not on the chain per se, but they keep the stuff there forever for free, so... why not? :)

And yes, you are correct in suggesting HiveStreams.Live and 3Speak for this. I know you knew that, which is precisely why you said it, but for others who see this and might be less familiar, here is the difference of the two:

HiveStreams.Live for real time live events where the audience attends live and shares a chat room with each other and the show host(s), and 3Speak for pre-recorded/edited cuts to be uploaded and stored as Video on Demand where you can watch as your schedule permits and comment accordingly like a Hive post, but video instead of text.