Right now someone, somewhere, is thinking of a way to use this to identify the ad portions in old podcasts and overlay new, perpetually relevant, dynamic ads.

This is already being done. Same as geo targeting dynamically inserted ads based on the IP of the downloading client.

They use the IP! That explains why I was getting Spanish ads for a few days after returning home.

I lived in CA and got advertisements for Ralphs. I spent some time in Sedona and all of the sudden I got the same advertisements, same jingle etc but instead of Ralphs it was Fry's. That definitely threw me off.

My podcast downloader is always on an IP from another country, I don't mind the ads nearly as much when I can't understand a word they're saying!

I'm fairly sure that most podcast platforms now include dynamic ad segments - I listen to a few and whilst some (usually where the hosts record ads themselves) seem to have static ads, others definitely have ads which are updated automatically

It's a shame - other countries' ads often strike me as quaint, hilariously awful, at best amusingly weird, and I'm willing to tolerate them to a point. But when an ad breaks in that's obviously targeted based on my location it feels ingratiating, dirty, offensive.

Yeah for sure. But is it being done for the huge back catalog of much older podcasts? Maybe the big players already have teams of people hunting for old ad breaks, but this could alleviate the burden.