The question of whether podcasts have hit the American mainstream is kind of like asking the same about Major League Soccer.

Both have grown for more than 20 years, but remain smaller than their counterparts in media or sports.

In the case of podcasts, advertising revenues grew by nearly 50% last year, to $708 million, according to an IAB/PwC report published this month. The figure is expected to grow by another 15% in 2020, despite the coronavirus crisis that temporarily put a dent in listenership numbers.

That remains much smaller than traditional TV's shrinking but still massive $61 billion for 2020, according to a recent estimate by GroupM.

Plus, "there remains this massive gap between monetization and the actual engagement of it," said Nick Quah, creator of the industry-tracking newsletter Hot Pod and host of LAist Studios' "Servant of Pod."

Still, the industry has proven attractive enough for traditional players to make significant investments. "The past six years has largely been the story of capital coming in and different legacy institutions finding their positions in it," Quah said.

Those six years cover the time since "Serial," the true crime podcast, captured enough mainstream attention to merit a spoof on Saturday Night Live. The team behind it, Serial Productions, will be acquired by The New York Times Company, it was announced last week.

Quah joined the Digiday Podcast to talk about that acquisition, Spotify's recent spree of purchases (including a massive $100 million deal with Joe Rogan) and whether there's a place for paid subscription podcasts.