From the article: "...replacing JPEG with something better has been a frequent topic of discussion. The major downside to moving away from JPEG is that it would require going through a multi-year period of relatively poor compatibility with the world’s deployed software. We (at Mozilla) don’t doubt that algorithmic improvements will make this worthwhile at some point, possibly soon. Even after a transition begins in earnest though, JPEG will continue to be used widely."
This is Mozilla's roundabout way of saying that they want to put off starting on WebP or JPEG 2000 as long as possible.
Not until WebP switches to VP9, which is not planned currently. VP8 does only support 4:2:0 chroma subsampling. Photoshop sets 4:2:0 only on JPEG quality 50 and lower, as comparison.
Only if other browser vendors adopt it, although IIRC WebP has hard-coded maximum file size limits that make it impractical for e.g. retina displays, let alone anything we might see twenty years from now.
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.
In addition to other concerns people have listed, I found WebP to be extremely slow – at or worse than JPEG 2000, with significantly worse compressed size. If we're going to go to the work of deploying a new image format I'd like at least a clear win versus the status quo, if not better features (JP2's tiled decoding would be perfect for responsive images if you could wave a magic wand to get browser support).
That's not hard: they put out a report months ago concluding that the claimed advantages of WebP were in reality slim to nonexistent, and that it could likely be matched and even outperformed by improved JPEG encoders...which is exactly what they're building now.
