Makes a lot of sense. Of course there are no universal answers here, and the whole, should I say, genre is evolving as we speak.
For the hypothetical, Tyson and Musk panel I would definitely read with interest. But all other things being equal, the primary driver of my interest would the I already know who these guys are and consider them quite worthy of attention and that they have something interesting to say, in response to reader questions or not.
Tangentially, reader questions do not have to be taken in real time - could be an intro/prep advance post inviting to submit questions or topics for consideration, for example. Same goes to selecting the panelists - perhaps give the readers a chance and/or place to suggest who they are interested to hear?
As to the possibility of intelligent conversation, I would very much say it depends on the participants. Take the recently mentioned The WELL SotY - it was an excellent conversation all right, from a diverse if not entirely unacquainted with each other roster of authors. Naturally, imagining, organizing and directing such conversations is an art in itself, as much (if not more!) in text form as it is in a talk show. This is something any one of us can get better at.
Finally, and debatably, perhaps there should be a post-panel discussion space? There's a danger it could devolve into nitpicking and sighs about someone's question or favourite topic not having been covered, but if we hope for the better, it could be a place where inspiration gives way to interesting discussion.