I think the bigger driver is that, due to it being the next PDF image format, most platforms will already be forced to add some form of support to it.

When literally every OS already comes with a form of libjxl pre-installed there is no good reason not to add support for it.

> you just truncate the output stream at the right proportion of pixel data

Does the format have explicit support for this? As in, is there any easy way to do, say, an exact Range request after reading the file header?

That doesn’t seem related to the codec itself but rather how you fetch said image.

Worst case scenario you should be able to add some smarts to the server and a query string such that the client can request 5% of the file or whatever simply by fiddling with the url.