Minus the “that the user could respond to” but isn’t that just show notes and/or chapters?
Those are already a thing as supported by, e.g., Overcast [1]. Overcast also has a function to share short clips, which I guess is similar to being able to link to specific points in a podcast. Podcasters don’t use the functionality available, though.
As a general rule content providers of any sort do not make use of functionality available in one content serving application, unless that application has near monopoly control of the market. Overcast evidently does not https://www.reddit.com/r/podcasts/comments/8ntp3x/podcast_ap... (unless stuff has changed drastically in last two years)
> MP3 chapter markers are supported by most podcast clients, including Apple Podcasts on iOS (provided you're on iOS 12), Overcast, Pocket Casts, Antennapod Castro, Player FM and more.
The larger RSS ecosystem already had semi-related standards for comments support such as Pingback/Trackback/Webmentions. It should be possible to reuse/recycle some such existing standards to the podcast world, if there were interest from different player makers.
This would of course also open up for other things like perhaps including resources at a particular point in the podcast that the user could respond to - for example links to relevant demos of technique under discussion etc.
And probably a greater development of different podcast players.