The real barrier to adoption is, for the time being, older browsers, anyway. Want to lose 20% of your potential market via IE in favor of some improved image compression? =\
True enough... though there are a lot of other ways this can/could make it in the interim... much like webp through various optimizing/ha proxies. I to think GPLv3 will hinder peopler even trying to look at or support the format though. There are some legal minefields that many won't cross when it comes to copyleft... even if they wanted to many are in jobs that wouldn't allow it.
You see how unsupported WebP is at the moment. Simply having a better compression ratio isn't gonna cut it.