Threaded voice memos would be cool. I have some friends who send voice memos like emails and I like it a lot. If we could converse more like email that would be cool. Maybe there's even something like a blockquote in threaded voice memo universe? (Low pass filtered sample of the original memo?) :-)
I agree with other commenters who are confused about the use case for this though. Podcasts are passive in my understanding. I don't listen to them but the people I know who do listen to them in situations where they really wouldn't want to be doing something interactive. (Like working on a car, or walking the dog.)
Edit: thinking about it a bit more, I suppose you're trying to set up a broadcast platform, not a communication platform. In those terms I think it makes more sense, but maybe using the words "conversation" and "friends" leads the mind in the wrong direction. You might try appealing to podcast authors directly?