Should we have a new *widely used* image format?

[ZiNgA BuRgA]

The 3 popular web formats, GIF, JPEG and PNG are really quite old (maybe not so much PNG).

Random info
GIF has been mostly superseeded by PNG, but unfortunately, there's no standard for animated PNGs, which is where one might still decide to use GIFs (ignoring IE6 compatibility).  MNG and APNG have tried this, but haven't exactly gained much popularity.  Besides, these formats do not do inter-frame compression (APNG is just a series of PNG images stuck together), so animations made with these can often be huge in terms of filesize.

JPEG is a very old format (like 20 years old) which is often criticised for screwing up images etc with its compression artefacts.  Basically all modern video encoders can beat JPEG at still image compression.  Despite this, it's still widely used, both on the web and in other places, such as digital cameras.
Attempts have been made to replace JPEG (without much success), such as JPEG2000, Microsoft's JPEG XR and Google's recently announced WebP format.  I'm not sure about the former, but Google says that it plans to add alpha channel support for WebP, so it may in fact attempt to replace PNG in some circumstances.  Anyway, WebP is based on a single frame of the WebM (VP8) format.
One thing I do wonder is, however, why not leverage this fancy video codec to get rid of the old GIF format?

Or maybe, when HTML5 is finalised, we could use the <video> tag to "replace" the <img> tag?

Disadvantages?
Now, whilst single frame video compression can significantly out-do JPEG, delivering better quality at smaller filesizes, it does come at a performance penalty.  That is, the decoder (browser) will most likely have to use more resources to display these formats.
This may make things more difficult on mobile phone browsers, for example.


So...
As webite administrators, do you think we need another image format?
Do you think Google's WebP will take off?