Everyone loves the "responsive loading" feature, but that's not even the novel thing about the format (JPEG 2000 did it even better — 16 years ago)! The novel feature of this format is better entropy coding. FLIF decoder adds interpolation to make incomplete scans look nicer than in PNG, but that's a feature of the decoder, not the file format, so there's nothing stopping existing PNG decoders from copying that featu…
> Note that it's generally not desirable to have FLIF used on the Web. A decent-quality JPEG will load at full resolution quicker than it takes FLIF to show a half-resolution preview. On the other hand, this allows browsers on metered-bandwidth connections to control bandwidth more effectively. Rather than disabling images entirely, this would allow loading a low-resolution version and stopping, and letting the user…
Unfortunately browsers don't do anything smart in terms of requesting progressive images, as there isn't an easy way to figure out how much of an image should be downloaded. So even on a 320x400px low end mobile device, you'll still end up downloading the whole the 2000x2000 header image - the only difference is it'll appear quicker as it is progressively rendered.