Easy enough to add a delay() each frame if your server is python/nodejs/PHP/whatever
Obviously the demonstrations that rely on server-side timing don't work through archive.org.
Edit: the format also supports region-of-interest decoding and I suspect you can make some cool maps or fractal images with both features. But I think they're not quite prioritizing implementing that right now.
I was about to say: I'm sure I've seen it work a t some point? I imagine it's a valuable thing to add for the web though. It would be really cool if you could use the same image source for thumbnail and full image, and the browser both just figures out how much to download based on pixel size and can resume previously partially downloaded images.
And yeah, the tiling isn't implemented anywhere yet, jxl doesn't really get enough funding for that. But it'll be really cool once it does since it also makes it really useful for giant images of geographic data. I don't know if it combines with streaming downloads as well, but it would be crazy cool if we effectively got OpenSeaDragon[0] support inside an image format