So here's the challenge. How would you listen to http://ntslive.co.uk/ via Chromecast? 

Dig around and you'll find the listen.pls file. In there you'll find a stream, http://stream-relay-geo.ntslive.net/stream which appears to play in a chrome tab. So you could then cast the tab, or maybe even re-purpose one of the Chromecast API example programs so it actually played in the Chromecast not by being streamed across from the laptop.

That's all a bit of a hassle. So is that Google's problem or NTS' problem? What about with Cast For Audio, because playing an internet radio station feels like a pretty strong use case.

At which point, I feel like Google should provide an official and supported solution to de facto standards like Shoutcast rather than expecting 3rd parties to support it.

At least if I was a middle manager in the Chromecast support group in Google, that's what I would do. ;)