Ira Glass Bullish on Podcast Advertising

Reported in Ad Week, Ira Glass spoke at SXSW yesterday and mentioned the state of podcast advertising:

It’s crazy; it’s amazing,” Glass said. “It’s unbelievable. It’s boom time. It’s a bubble!”
Asked if he thinks the podcasting bubble is actually going to burst, Glass said yes, but hopefully not for a while.
“I don’t know, hopefully not very soon,” he said. “But of course, like, audio—really? That’s going to be No. 1? When virtual reality headsets come in, we’re going to be listening to audio?”

Even with VR, the activities that cue my listening to a podcast aren’t going away: commuting, cleaning, cooking, winding down before bed.

But it does make me wonder, what is going to burst the $60 CPM ad bubble?