I think Twitter can be used for it. Also podcasts use RSS for distribution so whatever comment system is going to be centralized to some service and everyone has to decide to use it.
I'd argue that though this is an avenue your listeners MAY use, it's not one the author ought to encourage. It's far more valuable to try and drive traffic to a site you own and control.
The Atom standard tried to support commenting directly in the content feed. There was a threading extension to incorporate comments in the feed file itself and a publishing protocol so that you can post a comment in standard way from, say, an app.
If that caught on with podcast apps and publishing backends there would be no need for a centralized system. Unfortunately, the adoption of that was practically zero. To quote the Indieweb wiki [1]:
