Ah, that's interesting. I hadn't heard that before. It is a maximum size of 16383x16383[1], so it's more than practical for retina displays, but I can see the point about files in 20 years (for reference, jpegs can be 4x that in each dimension, 65535×65535).

I haven't heard that brought up as an objection to the format before, though. If it were really a fundamental stumbling block, there are likely ways to adapt the format around it.

[1] https://developers.google.com/speed/webp/faq#what_is_the_max...