What happened to Fling, Amazon's Chromecast clone on Fire TV?

Back in July 2015, Amazon announced a Chromecast-like feature for its own Fire TV streaming box and Fire TV Stick. The feature was called Amazon Fling, and it would allow existing phone and tablet apps to play media on a nearby television, just like Chromecast can. But over the last two years, that effort has languished. I can't find a single high-profile streaming service that supports Fling, and when I asked several streaming companies about it, their responses generally ranged from no comment to no interest. Amazon hasn't put much weight behind Fling, either.