Podcasts are trendy now for publishers, but Slate has been doing them for 14 years. Slate now has 25 podcasts that drew 180 million downloads in 2018 and expects to top 200 million downloads this year. Podcasting was 28 percent of Slate's overall business last year, and this year will be half of revenue -- eight figures.

"The hardest thing to do is to make something that is big," said Slate president Charlie Kammerer at the Digiday Publishing Summit. "There are 100-150 podcasts out that there that are big and then there are hundreds of thousands of podcasts that 8,000 people listen to."

Slate makes money from its podcast beyond advertising, using members-only episodes to drive consumer revenue in its Slate Plus program, which boasts 60,000 members.

One major challenge ahead for the podcasting world? Discoverability. It turns out that making a stellar podcast doesn't automatically get you listeners.