My dad's would probably have been like the audio narration of a Robert Carrier cookbook. Just utterly unselfconscious blither about seventies bistro cuisine and anecdotes about the hospitality industry. I reckon he'd have made it about two episodes without saying something massively racist.
Buckle up and prepare for the thrilling variety of 'Stanley-Gibbons Shade Variation and Perforation Flaws in Penny Red George V Postage Stamps', with support act 'Every 5 Day Test Opening Batsman Personal Best since 1882'.
I'm eternally grateful he's not also interested in trains.
Mine would probably be obscure musicology stuff, much like the papers he's still delivering (and chairing) at conferences...
I suspect he's too busy to make this happen, though.