Almost all podcast apps are still RSS based. Podcasts are in some ways the last mainstream bastion of RSS (despite Apple at one point trying to kill their reliance on RSS, but giving up and going back to RSS).

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.