The app is definitely not their focus, in particular podcasts where the app becomes very slow and crashy as you get hundreds of episodes per feed. Those features still are not present.
ABS does support RSS enough that you can hook a preferred podcast app up to your "local podcast mirror" and only use the ABS app for actual ebooks.
Json messages passed through stdio. There are also SSE servers that will run over http. It's more complicated than rest since you use http to open a similar json messaging channel